Part of the issue with collision is that the Dwarves throw things so high into the air, if other Dwarves are too close behind the full stacks collide when the previous stack is rising/falling. That could be fixed with timing, maybe an isolated throw has barely any height with throw height being progressively higher down the line to avoid colliding with previous stack.
It would also help if collection was faster when capacity is barely filled (and by size/weight), or similarly throwing from further away (and adding overshoot as that collects anyway) rather than taking it to the right, inventory combining/swapping etc. EDIT: I do see that gorilla arms sort of do this, but they also sort of make the problem worse (until it happens again further away from the mountain).
I could see not having them bunch up being part of their behavior as well so 4 don’t get knocked out by 1 rock (also collecting from the middle of a pile, not just the edge), using speed boosts (or slow downs) for this and attempting to avoid projectiles. Gem rush seems like it’s wasted when they’re still collecting stuff out of a large pile (late-game carry capacity at least). EDIT: Even if it’s just the short duration, in the late game I do see speed lines on when they’re not moving (in the right corner, I suppose it could increase loading speed but it really doesn’t seem like it).
Also, have prestiged multiple times and that still feels painfully slow. Partially because cost scaling and small upgrades, but base speed likely should be higher (so runner speed upgrade is more impactful).