[dx034]

But even a 20GB file? Streams are much more compressed, but I found files >20GB or so to be pretty much the same quality.

Which doesn't really matter though, you can also find 40GB files of most movies, they should (if encoded well) definitely match the quality.

[cbg0]

It varies quite a bit, I see a lot of banding in various scenes on my TV with 20GB WEB-DLs compared to an actual 4K BR rip.

[rosndo]

In most cases that is to be expected because WEB-DLs tend to be poorly encoded. You should be looking for a remux.