If you're running purely Photoshop or Lightroom and not much else at the same time, a Mac Pro 7,1 is not going to be much if any improvement for you. Both apps are pretty terrible at using any more than 5-6 cores and have minimal GPU use. I have both the 16" MBP and a new MP 7,1, and I can tell you that right now Lightroom is pretty much identical in speed on both. That's both an indictment of Adobe and how lousy their software is in terms of optimization, and a testament to how much of a powerhouse the 16" MBP is. The few areas the Mac Pro is faster is when doing things like bulk imports and exports of large number of files. At those tasks its fast enough to be a noticeable improvement.
In my case I use a number of other applications simultaneously and I do regular bulk imports and exports of large number of files, so the overall value of the Mac Pro is worth it to me--but if I only did LR or PS, I wouldn't recommend it at all. You will just end up with a ton of unused horsepower.
As for my use case, I am using Lightroom all day long, and most days I will import and export several hundred Sony A7R IV raw files, which are generally pretty big files. I also do a lot of image stacking in HeliconFocus and it now supports the AVX-512 extensions so it's blindingly fast on the Mac Pro. Because I often have three or four applications open at the same time while doing the image stacking, I can also chew through RAM--I've been averaging around 100-120GB at any point in time. For those reasons, the Mac Pro is worth it for me, but Lightroom and PS alone? No.
FYI, the ProDisplay XDR is just gorgeous and works like a champ on the 16" MBP. You'll love it.