Well, it's more like it's going to make certain problematic systems on the current aircraft (yes, they are being dealt with, but...) more problematic. The other aspect is simply that to fit two engines the size of the F135 with decent aerodynamics and other considerations gives you an aircraft that's once again the size and weight of the F-22. The F-35 is intended as a mid-size fighter, not a heavy fighter. Mind you, a new heavy fighter combining the best of the F-22 and F-35 would be a very dangerous beast indeed; might be interesting to see what might happen if a "scrapped" F-22 was salvaged and a whole lot of upgrades from the F-35, and various other aircraft, were added.