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Dang that does look bad.

Maybe the next XR if apple continues the model will be better. Apple might just fix the issue you never know.
 
I do find that to be surprising as well...

Must be down to processing. Have you tried a self processed RAW shot on the XR to compare?
 
Seems like my careful attempt to preempt that objection was lost on you.

"The big difference is that the SE's noise is relatively uniform and not that noticeable under normal viewing conditions. The XR, on the other hand, is somehow managing to make it into huge, ugly chunks that do become noticeable on normal sized displays."

And how do you suppose I noticed this in the first place? If it hadn't been visible in normal viewing, I would have had no occasion to "pixel peep".
The point is on my max and my desktop monitors the first two pictures look nearly the same. You played with the brightness/gamma in the 4th picture to make the picture way to bright, in a way where you are blowing out highlights. You didn't post the specific ios version however, apple supposedly ratched down the processing in later ios releases.
 
The first two aren't even remotely close. If you can't see it, it'll be because of your monitors and/or viewing environment. I said I deliberately blew out the second two to make it clear what I'm referring to, so I'm not sure what your point is there. Both phones were on the latest version of iOS.
The Xs max with a supposedly calibrated oled screen doesn’t show much of a difference in the sweaters. Blowing out the highlights will accentuate the bad qualities. Anyway that’s my take on it.
 
Well, part of the “problem” is that the XR photo is more underexposed, compared to the SE (higher ISO and higher shutter speed, more than required to “equalize” the difference between f2.2 and f1.8). Cellphone cams, with their insanely small pixel pitch, need enough light to achieve sensor saturation or else (because of the tiny tiny pixel pitch) the poor SnR (signal to noise ratio) really shows it’s ugly head.
 
All the new X phones picture look like crap when you zoom in to pixel level. It's easy to tell what iPhone was used to take a picture. If it has that noise added around the pixels, it's either an XR, XS, or the Max.
Clearly  made a design decision to have the pictures look best on an iPhone when not zoomed in.
 
The only way to know what will work for *you* is to try them yourself.
And since you said even the XR does ok sometimes then your best bet is to get one to try within the 14 return window and if it sometimes doesn’t work for you, return it and get the other one.
 
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