Good points being made that Yesterday's Enterprise isn't necessarily the inevitable outcome. As stated, we don't know enough on how the Klingons were able to get the upper hand in the first place, or how their side was doing.
As of Way of the Warrior, it seems to me the Federation overall has superior tech, but Starfleet is geared more towards exploration and peacekeeping, whereas the Klingons train for war. So, I think the Klingons offset the tech advantage out of tenacity, making the odds even. The Federation ships probably have the edge one on one, but the Klingons often have a cavalry of sorts where BOPS travel in wolf packs to make up for that, and the Klingons do have a cloaks on most if not all warships, as well.
The Feds would implement their own cloak eventually, but the Klingons could potentially win key victories before the cloaks were pressed into service by the Fed. Then again, because even though the Feds would be using the cloaks against the Klingons, that would violate the Romulan-UFP treaty, and they may not want to risk angering the Romulans and possibly fight a 2 front war. So, it is possible they may abstain from using cloaks.
I therefore voted stalemate, but lean towards the Klingons slightly, though if they were able to pull out a victory, I would think it would be a Pyrrhic victory.