I'm not at all that impressed with Patton. His "spirit of leadership" ie. dashing moves, was much more suited to the Axis situation where you had all to win and really nothing to loose than it did to the wallies, where being out on a limp was the biggest threat. His biggest feat, turning the front of 3rd Army at the Bulge was mainly a splendid staff work. If I would want him somewhere on allied side it would be instead of Mark Clark at Salerno - charge with what you have and don't wait for the enemy to stiffen up.
Rommel IMHO did well with what he had but basically was in an increasingly impossible situation.
On top of my "replace" list would be Gamelin with anyone not expecting the enemy to follow your own plans - or at least conduct a thorough air recon over the Ardennes.
Next is of course Percival and/or Brooke-Popham.
The first with someone daring to actually prepare the defence of Singapore even if it might scare the population and the second with someone not being so "bullied" by Churchill's warnings about not provoking a war that he ignored clear intelligence on a Japanese attack.
The matter could perhaps have been solved by sending Dill to USA ahead of schedule (Dec 41) and replace him with a personality like Alan Brooke actually able to withstand Churchill's worst fantasies. The Imperial General Staff in early 1941 had proposed Malaya and Singapore be brought closer to the demands of the Matador Plan, but Churchill wanted everything focussed on/in the Med and thought a couple of battleships would do the trick. It would only take a fraction of the losses in various futile OTL operations (Rubarbs, Greece, NA 1941 etc.) to beef up the defence of Malaya and Singapore enough to make the job impossible for Japan. Not just because of the increased means of defence, but because the local allied leaders like Percival and Brooke-Popham think they have a chance - in OTL they had given up beforehand.
So perhaps the most productive PoD would be having a roof tile hit WC himself in late 1940!