I installed the latest updates of LrC (version 10.1) and Ps (version 22.1) on macOS Big Sur 11.0.1 and the icons of both applications differ considerably in size. LrC's dock icon has been adjusted to the default size of the new macOS Big Sur icons, which is slightly smaller than the ones from the previous OS (Catalina). However, Ps' icon has not been adjusted and still has the slightly larger size.
This is particularly visible (and annoying) when both applications have their icons displayed in the dock.
The Finder's icon size settings are the same in both cases, yet the difference in icon size is considerable.
I'm having the same issue as well! I just downloaded the apps onto a second laptop and I updated to big sur just before I did it, and photoshop is way larger than the rest of my apps. However, I had the apps downloaded on my mac before I upgraded to Big Sur (on my main laptop) and they all ended up the same size. I wonder if the order you download/update things has anything to do with it?
I had exactly the same issue as well, which drove me crazy, and I found an acceptable solution. It consists in manually changing the LrC's app icon, so it has the same size than the other Adobe CC app. To do this, download the app "Pictogram", which enables you to change app icons by any other png image.
And then, replace the original icon with one you've resized in Photoshop so it has the same size as the others.