Golden Souls 3 and to an extent 2 and 1 use a lot of features Gzdoom offers that other sourceports don't, and that's because Gzdoom is its own thing at this point, and it's so advanced that it can be used as a proper engine for indie games, it's miles ahead compared to every other sourceport in terms of what the developer can do, and I assure you that this project would not by any chance be possible on anything else.
A GTX 760 as a minimum requirement isn't so absurd, considering it's a 10 year old GPU at this point...