Mostly true, but the weird edge case I run into is workspaces. Since they seem to be independent of and not backward compatible with git worktrees, there is no fall back to git for submodules within a workspace.
We still use submodules in a number of places at work so it’s a bit of friction for me. Other than that, I’m rapidly becoming a jj convert.
Ahh, so workspaces don't currently support colocation, aka "put a .git directory in there". So that's what's up there. Interesting corner case! I know upstream is working on it.