Ah, I misread and thought you had cleared it just not without God Mode. Yeah, you need to beat a run to unlock the pact. The weapon aspect upgrades can be helpful but they get increasingly expensive (excepting the default aspect) and mid-run boons will probably have far more of an impact by the end of a run.
What mirror skills are you currently using? It might be that changing those up could help a lot more!
kazanova_Frankenstein wrote:Though i assume the sheet music and cosmetics are just that? They do not offer any meaningful progression?
Some of the cosmetics have stat-tracking effects e.g. the aquarium reports how many fish you've caught, the pool in your bedchambers reports total kills and escape attempts.
Two character stories that I can think of (and the gameplay item unlocks behind them I believe) rely on cosmetic unlocks:
Dusa asks you to refurbish the lounge and
Orpheus requires you to unlock the harp.
It's not really anything you need to worry about too much though and the vast majority is just cosmetic.