So after some testing, I'm concluding that the crowd noise not being affected by volume sliders is a web build issue, as on the PC download build you can set it with volume sliders just fine. It seems as if the web build has an issue with different channels using the same mixer; the crowd noise plays in a "BG_sound" channel which uses the "sound" mixer, but somehow the "sound" mixer on web doesn't affect any other channels besides the main sound channel (blegh).
In the upcoming update, I've reduced the volume pretty significantly, and I've also applied the bandaid fix of registering the crowd sound as music, which is weird but also you can adjust its volume in the menus now. Furthermore, I've did a full pass on most of the game's sounds, adjusting volumes and removing unnecessary sounds as needed. It should be pushed soon. Thank you for your feedback!
(deleted this once to fix a typo whoops)