But the graphics engine does not need to be overhauled to accomplish this, nor would it even be remotely feasible to spend time and money on at this point, in what is already the best looking MMO around.
The server problems and the engine problems are separate. Together they create a feeling that I'm walking through a swamp while playing.

Just because the engine can create ultra HD graphics doesn't make it good. A good engine can achieve that and perform efficiently for both the players and developers. This engine doesn't.