I've been using PS for a long, long time, and something annoys me in the perception of PS vs LR -- destructive vs non-destructive editing. A big deal about Lightroom has been that its edits are "non-destructive," that the original file is never touched, and the changes are kept discretely in a separate history folder away from the original. That's fine, but as a PS user I find destructive vs non-destructive meaningless in practice. Here's why: When you open a file in PS, like in LR, you are not touching the original. You are copying it from your storage medium -- hard drive, USB drive, cloud -- to local RAM. It is with the RAM copy you are working, not the original. You can mess around all you want with the RAM copy, and the original will remain untouched. It is only when you hit SAVE that the original will be changed -- the RAM copy will overwrite the original. Now, for a JPEG, that SAVE will be destructive, because JPEG uses "lossy" compression that loses data whenever the file is compressed and/or recompressed, which happens when you open the file then recompress it when saving it again. (This does not apply to just viewing the file image. Again, you are just copying the original to RAM, then closing the RAM "file," which goes out of existence. OK, there may be cached RAM somewhere in your sys files, but that's not relevant to this discussion.) For TIFFs, BMPs, RAW and other non-lossy files, you can SAVE them, then say, Oops, go to the top of the History pane, which always retains your opening step, even if you've "run out" of History steps, hit SAVE, and get your original back completely intact. Also, if you hit SAVE AS, then you will make a different file from the original, in a subfolder to the original's folder called, say, New. This is always good practice at the beginning of your workflow. Then, no way, now how, will your original be messed with. Oh, but you say, you're using up a lot of space! That may have mattered in the past, but in today's world of cheap terabyte drives and limitless clouds, it really doesn't matter. So, choose between LR over PS -- maybe for workflow efficiency -- but not because of "destructive vs non-destructive". That argument is just not very compelling.
If you only stay within Lightroom and 'raw' images- it is non-destructive. No debate. Raw data in a file is not altered.
Once a photo moves to a 'pixel' format- then Yes! I agree with you. All bets are off.
A 'pixel' image can be changed in so many ways, by so many different programs. Lightroom does not protect you from pixel editing with external programs, including Photoshop.
But even a JPG image file can be edited in many ways within Lr using Virtual copies, history, and snapshots, and the original image file is un-touched when you export a 'copy'.
So you can prove the 'Non-destructive Myth' wrong if you really try!
I'e said this for a long time. You can work perfectly non-destructively in Photoshop and go back to a pristine original at any time, just like Lightroom. Reversible vs. non-reversible doesn't quite work either - same argument.
I just call it parametric editing and pixel editing.
If you're thoughtless you can turn a file into mush in Photoshop. But no need to.