fwiw DC is essentially the same situation as PR in this regard. DC would essentially be a blue city-state (state) which is also why DC statehood resolutions always fail.
It's an open joke in DC if you ever visit there the official DC license plate has "end taxation without representation" on it.
You are right to point out the problems with getting it passed. I would just say we need to stretch our political imaginations. Let's also remember that when the Constitutional Convention was originally convened no one thought it was going to create a new constitution - it happened sort of by accident as circumstances changed. The original purpose was to make revisions to the Articles of Confederation.
I'll put it another way. We are far from the bottom here. This system can and I believe will inflict more dysfunction on us in the coming years. A constitutional crisis is not unthinkable anymore for a variety of reasons. A modern constitutional convention might be one of the few ways of getting ahead of it.
Perhaps in such a future situation then, small states can be convinced to amend compromises they may otherwise have never considered.
You could also just do away with bicameralism, which was proposed at the original convention. Also remember as originally written the population of the states did not directly elect their senators. Thus there is already amendment precedent (17th) for making major changes to the Senate.