in prototypes/entities.lua
line 140 and 145 are mismatched.
0.38 should be on the 60/s line and 0.5 should be on the 84/s line.

60/s has 2 very fast inserters. 84/s gets 4 inserters, so they are individually slower.

Well I had an issue where the mk2 rapid loaders werent eating a full mk2 rapid belt and when I switched these lines, the rotation speed is more proportional to belt speed since originally it was mk1 10000ish and mk2 8000ish
After this the loader ate a full belt; before this it did not