You may be right. But that (R) may be just the seat that puts the gavel in the hand of a new Majority Leader and in all the committees. That is the larger point that is too often missed, I think. That one (R) can possibly decide which Supreme Court nominee moves out of the Judiciary Committee, for example.
It comes down to who is setting the agenda.
If that were true than you an blame the RNC for not supporting republican candidates.
If the democrats retain control, it's the RNC's fault.