flasks are really boring in poe 2

Yeah, perhaps on one of the optional quests, or also with incorporating charms, whereby it is possible to exceed 3 currently without benefit (3belt + 1quest).

I still think they need some variety on the mods to justify making them worth picking up and crafting on.

good. Not everything has to be exciting min max sweat gameplay.

Maybe, I prefer that the flasks have more character, but otherwise, make them drops less, so they are more valuable. Do not need 100's of flasks dropping in the campaign if they are all very similar. Without a vendor recipe to upgrade them with, they are basically just a transmutation shard. 3 to 1 sideways is not even available until mid campaign, so having heaps of them dropping doesn't seem necessary with the current mod pool.