I could possibly make my own thread about this, but didn't want to do a huge write-up and just figured I'd tag along with the last few posts detailing the iPhone 11 Pro and whether it can be a viable replacement for a dedicated camera.
My brief take on it is: it can't.
To be fair, I just picked up my iPhone 11 Pro today and only used it for a few hours. I do have manual camera apps that produce RAW files, but I stuck with Apple's native camera app for this one. I used it in middling to poor lighting, which is what my dedicated cameras routinely deal with and where most of my photos are made. iOS 13.2, which enables the "deep fusion" neural processing that is supposed to help in this type of lighting specifically, was installed. It's being compared against an Olympus E-M1 Mk2 (a high-end, 20 megapixel camera from Olympus that uses a µ4/3 sensor, which tends to be trashed amongst the photography enthusiasts for being on the smaller side and exhibiting more noise in images) and Olympus' highest-grade lenses; and a Fujifilm GFX 50S, a 50-megapixel medium-format camera that is professional-level and accessible to enthusiasts (Fuji's medium-format lenses are not classified into high-end or low-end; all are regarded to be about as high-end as you can get). Both cameras use sensor technology that is now about 4-5 years old, but still very relevant today. With both cameras I shoot in RAW and process the images myself in order to get the maximum imaging capability out of each.
So first, the good: it's definitely an upgrade over my iPhone 7 Plus. The 7 Plus displayed a mixture of luminance and color noise in poorer lighting, whereas the 11 Pro seems to just have luminance noise. Out of the dozens of shots that I tried, including an incredibly dim scene that utilized a three-second "night mode" exposure, I couldn't find any color noise. As far as details go, my 7 Plus was capable of some impressive detail in perfect lighting, but detail quickly dropped off in any poorer lighting than that. The 11 Pro seems to retain the impressive detail in slightly less than perfect lighting, making it more usable.
However, the amount of noise and the smearing of details and skin tones - issues that made me start reaching for my dedicated cameras far more often over my iPhone 7 Plus once I recognized them - are still present. Deep Fusion was supposed to improve detail on things like hair and fabric, and I think it's working for the fabric; for hair it's a bit mixed. However, skin tones are the big issue that I care about, and there's not much that seems to be done for them. It's less apparent if your photo subject is small in the frame; if you're filling the frame with a face then this problem quickly becomes obvious. Similar to my 7 Plus, the "telephoto" lens option is the worst offender when it comes to noise and loss of detail, which makes sense. As telephoto lenses are more vulnerable to the movement of your hand, the iPhone is probably using higher ISOs more aggressively with the telephoto lens; higher ISO = more noise = need for a stronger noise filter to make it less apparent = less detail.
Overall operation is faster and more pleasing compared with my 7 Plus, as one might expect, although I've found a weird glitch in which the wide-angle lens inconsistently adds output from the ultra-wide to the viewer (and not perfectly, either... despite "photos outside of the frame" being disabled) - probably a software glitch that will be ironed out later. Portrait Mode is more viable to use without as much planning, although I'm not sure how it'll fare against my toddler who is frequently in motion. (Only one of my two cameras, the action-oriented Olympus E-M1 Mk2, can reliably keep up with him when he's moving about.) Night Mode still had a ton of noise but it honestly impressed me that the iPhone was capable of producing such a photo at all. I anticipate that the photos in perfect lighting will be just as good as the 7 Plus, if not even better. 4x6 prints wouldn't be a problem; depending on how things go, larger prints are a possibility. However, the most demanding use I have for my photos is using them as a desktop background on my 27" "retina" monitor, and the iPhone photos won't cut it. A large part of it is a limitation of being 12 megapixels in resolution; that's just a size that demands too much. Even the 20-megapixel E-M1 Mk2 doesn't always provide images that can stand up to that.
I wouldn't have upgraded my phone if it weren't for the addition of a third lens in the form of the ultra wide. I do have an ultra-wide lens for my dedicated camera, but I don't use it as often as standard- and telephoto-length lenses. It's kind of exhilarating to have ultra-wide capabilities on the phone, but there are some caveats. The aperture is smaller (more sensitive to lower light levels). Someone on this forum also posed a question about whether the lens is actually a fixed-focus lens, meaning that it doesn't actually adjust focus. Based on my testing that does seem to be the case: they're relying on the fact that the depth of field is so wide that almost everything will appear to be in focus at all times. The thread discussing this pointed out that images appeared a bit softer from the ultra-wide compared with the other two lenses, and that could be why. Additionally, the ultra-wide didn't receive any image stabilization, likely a choice made because the shakiness of our hands is less apparent with a wide angle of view. Perhaps being able to be focused, and having image stabilization, are features that will be added in future iPhones.
The #1 usage for my iPhone camera app - and an area where the iPhone is pulled out over my dedicated cameras - is for video. Video looks nicer with the dedicated cameras (there's that cinematic appearance associated with a shallower depth of field), but while my cameras are stuck encoding video in H.264 the iPhone encodes in HEVC (H.265), which practically cuts the file sizes of video in half with no perceptible loss in quality. Video is also a lot more forgiving when it comes to loss of detail and image noise (particularly as I stick to 1080p instead of 4K). Having the ultra-wide lens option adds a lot to video; there were many, many occasions with my 7 Plus where I'd have to hold the phone to the side of my head or at my shoulder, half-guessing if I was getting the right thing in the frame, because the lens wasn't wide enough to fit everything that I wanted. With the ultra-wide angle lens option, I can now comfortably hold the phone in front of me and get it all, and more. There's the characteristic distortion associated with the ultra-wide, same as on any camera, but that's OK.
Overall, I can say that I don't regret the purchase. It'll give me more capabilities with my videos. As far as photos go, I'll be tempted to use it a bit more if I don't have my camera with me, but I don't think this will make me feel any better about leaving home without one of my dedicated cameras. Carrying a camera around isn't a hassle for me, and it actually feels easier for me to quickly round off a shot with my camera than to bring out the iPhone, fumble to open the camera app (despite using the gestures, and now the dedicated button), and then get to it.
If you have an entry-level camera and only use the lens that came with your camera, if you have a dedicated camera and only shoot in JPEG mode, if the vast majority of your shooting is in brightly lit situations, and/or if your primary use for photos is mostly sharing in text messages and on social media, then I could certainly see how the iPhone 11 Pro would represent an opportunity to kick a dedicated camera to the curb. Even if you do more with your camera, I absolutely agree with the saying that the best camera is the one that you have with you. I favor the ergonomics and image output of my dedicated cameras compared to the iPhone, but even the best dedicated camera does someone no good if it's just sitting on a shelf at home. No matter what camera you have, the iPhone is bound to be more portable, and it's true that we all carry our phones on us at nearly all times... but few can make that claim about their cameras, including me.
iPhones still have a long way to go, but it's quite impressive what they're capable of now. It feels like their rate of advancement is faster than the pace of dedicated cameras. I'm not sure that they'll ever fully be able to catch up, but with computational technology padding the way, I wouldn't bet against them.