This is an important point that too many people ignore.
The reason the GOP has done all these bad-faith and dishonorable things is to maintain power and minority rule without moderating to appeal to the voters.
The answer to their bad-faith assholery is not to tie one hand behind your back and worry about 'what they will do if you do this'. They're not limited by what you do. They're dishonorable.
Those changes, things like restoring the integrity of the Supreme Court, democracy strengthening voter rights protections, representation for places like DC, would mean that the Republicans would have to appeal to the voters again to have power. This means that getting the power to 'do the same thing back' involves stop being the bad-faith actors they currently are.
The Dems have to stop worrying about 'seeming reasonable' and being 'responsible'. The GOP dictated the terms of this battle, so screw them. They don't actually care about it, neither do their voters, but they are the minority.