Any given snapshot has a linear history, so it should be as bisectable as the rebased equivalent. What am I missing here?
Not sure what you mean. The key thing of merges is that they... merge... two histories.
A git history graph tool shows that clearly then.
A bisection has to choose whether to go left or right.
Any given snapshot has a linear history, so it should be as bisectable as the rebased equivalent. What am I missing here?