Making DC a state is a horrible idea not just because it would vote Democrat. There is a reason why it was done the way it was. It already has outsized influence as it is, and giving it two senate seats and whatever house seats it would get, would only give it even more power. If anything we need to dial back its bad influence.
DC is not denied the vote, its still votes for city offices, for president and other offices.
I don't see Puerto Rico wanting to become a state, it would lose too many goodies it gets from mainland taxpayers.