Act 3's issues aren't GPU bound, it's entirely CPU bottlenecked. It's likely someone with a slower GPU won't see as big a drop in performance in act 3 as you, and it's likely you don't see any performance gain from using DLSS in act 3. My 2080 Super was sleeping through it even at 3440x1440 on ultra while my Ryzen 7 3700x was getting thrashed.
When you buy digital media, whether physical or digital, you are buying a license to be able to view it whenever you want. You do not own the media. You don't own the rights to that game just because you have a physical copy of it, you don't have access to the source code, and it is still riddled with DRM. The same applies to movies and music as well.
At the end of the day, whether a piece of media is stored on a Blu-ray/DVD or an HDD/SSD makes little difference. If all ownership means to you is being able to access the media you've purchased a license to consume regardless of its online status, then archive it. Your SSD or HDD is as much a physical media as a Blu-ray disk.