A warranty replacement is as good or better than a genuine Apple Refurbished iPhone and those things are top notch. In my opinion Apple refurbished iPhones are BETTER than a factory new iPhone.
I purchased a warranty replacement iPhone 6 Plus on Swappa 6 years ago (advertised as unused) and that iPhone was and still is flawless.
I recently purchased an Apple refurbished iPhone 8 Plus directly from Apple and it was immaculate looking - like brand new- and it works flawlessly too.
Those two experiences of course can’t predict the future, but so far I’ve hit two home runs.