> If we could just get off the tree-of-diffs model.
That's exactly what Git's innovation was, though. It doesn't work with patches or diffs, it works with (essentially) snapshots of the tree, and how they are related to each other.
You need the commit history, because that's the fundamental point of the VCS. Linux devs need to be able to demonstrate the provenance of each piece of code in the tree. That's the problem that git exists to solve.
> it was a bad, but performant copy of monotone's DVCS UI/UX.
I don't think the UI is what makes git, git. AFAIK Torvalds didn't put much thought into workflow or UI design - that evolved later. It's what goes on inside .git/ that's the innovative bit.