OP argues that branches aren’t “just refs”, they’re a sequence of commits. I’d argue that a ref _is_ a sequence of commits. (Or, to be pedantic, it uniquely identifies a sequence of commits.)
A commit contains a sequence of commits, in fact (unless it is the root commit). So a ref is just a single commit, which then contains parent commits. The branch model really falls apart if you ever do a more complex merge or rebase.