"And correct merge-commit messages" -- I've NEVER seen those. In 99.99999% of projects, this is what you'll get:
That doesn't mean using merge-commits is wrong, that means people write bad commit messages, which you already complained about.
I fear you may be terribly misunderstanding the point of atomic commits and readable commit messages. Everything within a merge commit will still come up during a bisect, for example. If the commits are non-atomic and/or they are badly written, that is still an issue.
--first-parent hides the problem, and adds a new one. I'm not sure what your thinking is. Once again, what's more readable to you of all the screenshots I linked?
#!/bin/bash
bad=$(git rev-parse "$1")
good=$(git rev-parse "${@:2}")
git bisect start "$bad" $good
filter=$(echo "$good" | sed 's/^/^/' | cat <(echo "$bad") - | xargs)
comm -13 \
<(git rev-list --first-parent $filter | sort) \
<(git rev-list $filter | sort) \
| xargs git bisect skip
For anyone unfamiliar with git extension scripts: You should be able to put it in an executable (`chmod +x`) file (say `git-bisect-branch`) in your $PATH to make it usable (`git bisect-branch $bad $good...`).