I also have this issue! :(
Thanks for making the thread, OP!
Btw, I'm playing with the game installed on my external hard drive, with an Xbox One X linked to a 1080p tv without HDR support and with the language/subtitles selected to my native language (Italian). To all the folks who have posted on this thread, what about your settings? I wonder if these specific settings may explain why some people don't have these issues, or if everyone have these problems but they just can't notice them...
I've tested on a 1080p tv, on a 4k tv with HDR, installed to the internal and on an external.
I uninstalled and re-installed and even tested on a second XB1X.
The results were the same every time:bad framerates.
I think complaints aren't widespread because the majority of players played through the campaigns before the framerate destroying patch was released and moved on to multiplayer, and the new players just assume it's always been like that and 60fps is too much for the hardware, shrug and move on
It's also possible that it only affects the XB1X , and the majority will be playing on base hardware.
I'm setting up my original XB1 and testing today, and i'll post my findings here.