You can 100% the first three Spyro games in about 9-12 hours each. The first one can be done without any backtracking, even, since you have the same move set throughout.
I believe modern games take 100% runs way too far. I enjoyed 100%-ing the 3D Mario games… and then I got to Odyssey, and it was such a ridiculous slog that I couldn’t get much further than the standard ending.