Ok, so separation of powers, and related ideas like checks and balances, are supposed to be about each branch having its own sphere of authority that it can use to check the power of the others. It is not about how the two branches can gang up on the third in order to sabotage and cripple it.
On the second point about legislating from the bench, why is your method better than just appointing judges that won't do that? Yes, there might be some short term advantage in it, but at the end of the day we actually need a functioning, independent court system, and it's not even clear why an activist GOP SC is actually a good thing. The GOP was all onboard with the patriot act and used to place a great deal of trust in CIA and FBI, which we now know to be mistakes.
I don't share you apparent confidence that now we've wised up to that, we have no more blind spots and can totally trust an activist SC to work in our best interests.