I believe mbin stopped merging kbin changes, probably either when they had their fallout with ernest where he pushed unfinished code that caused issues, or when he started his refactoring which I've seen some mbin contributors dislike because it requires changes on their side too.
Either way, there's definitely features missing on mbin that I know are in the kbin source, like the sort options on profiles. Collections are definitely there too.
when in theory they all use 0.10.1
First of all, there's no way this is true for mbin. It's a fork, it has its own versions.
Fedidb says most instances of mbin (on its first page of instances) use version 1.5.3, though kbin.melroy.org uses 1.6.0.
But also, hasn't kbin been 0.10.1 since forever even before ernest added all the new features? I don't think that version string means much if anything.