I mentioned back in post #5 of this thread about traffic jams. Attached is a partial screen capture from my Netgear router information showing the 6 devices I have attached via ethernet and the 21+ devices I have attached via Wi-Fi (both 2.4G and 5G). Traffic jams can definitely occur, even with a fast 200 Mbps service like I have.
Wired via ethernet I have my ATV 4K 2017, Fire TV Cube 2nd gen, Fire Recast, one Amcrest surveillance camera, MacBook Pro, and Mac mini.
Connected via Wi-Fi are 21+ devices including several Kasa smart light bulbs and smart plugs, four Alexa speakers, three Amcrest surveillance cameras (two using 2.4G and one using 5G), two iPads, one iPhone, and an assortment of other smart devices. That is quite a lot, but a typical house these days can easily have that many smart devices now that they place Wi-Fi capability into so many devices. Add to this crowded Wi-Fi group of devices all the BT signals which are also 2.4G, and radio waves are bouncing all over the house all the time! Interference is going to happen, traffic jams are going to happen, poop is going to happen!
A couple days ago I was trying to stream Hulu live TV on my ATV 4K 2017 and I started getting the little gear spinning as it briefly tried to load the stream. That is unusual. After a while I thought to check my connection and found that I had apparently bumped the ethernet cable connector on the ATV 4K and it wasn't connected properly so it had switched to 5G Wi-Fi. I snapped the ethernet connector back into position and the problem went away. Routers only have so much bandwidth to spread out and route to all the Wi-Fi devices, so you might not always have 25 Mbps going to the ATV 4K when you need it. With ethernet, you have a much better chance of getting the bandwidth you need when you need it.