Hey, I think this is a really cool idea and would love to see u expand on it. I love the dropper mechanic because it is a new kind of incremenetal game mechanic to consider that we have not seen before.
I think the key to the compelling experience here was managing: what is the optimal amount of gem factories to have, so that the bin is completely full when it drops but does not overflow? And then what composition of those gems is the most profitable? Because after a while it becomes counter productive to even have quartz factories as they prevent more valuabel gems from taking up space. That is a cool little incremental puzzle to consider.
But the problem is, it seems like you are too scared to inconvenience the player, and you give the always-open upgrade within like 15 mins. Then it just becomes another old incremental game where you just check in every once in a while and buy the next tier of buildings and upgrades. Very boring and laggy so i just stopped after getting a few diamond factories.
IMO you should redesign this game around an incremental system of upgrades for the auto dropper and the pit size, instead of how right now there are only 3 upgrades for each. you can take a look at Idle Bouncer for an idea of how that works. Then it would be quite compelling to play for a long time, as the player would have to be constantly recalculating that key question i mention above.