Your final paragraph is simply false. If there is no better manager out there, then sacking the existing one isn't a sensible idea. If there is, and our current manager was as bad as you say, it should be trivial for you to make a case for another manager who would come in and do a better job. Unfortunately nobody has been able to do that yet, which includes you so far.
If you can make a good case for a replacement then you can get me on board, genuinely, but it needs to be deeper than just "sack the manager and get anyone in".