From extensive reading on the early SWPA aerial combat, it appears that most Allied first line fighters like the Hurricane, Spitfire V (or earlier marks), P-40, and P-39 were able to just hold their own with the Zero. That is, in fighter on fighter combat neither side held any great advantage. The Zero could out maneuver the Allied fighters but they proved difficult for a Zero to kill and extremely dangerous if they got a shot in return.
The earlier pre-war and obsolesent types that were in service early in the Pacific War like the Buffalo, CW 21, P-36 or P-35 were simply outclassed by the Zero.
Interestingly, none of these types was outclassed by IJAAF fighters in operation early in the war. Neither the Ki 27 Nate nor the Ki 43 Oscar proved in a class equal to the Zero. While the Oscar was even more maneuverable than a Zero its armament of just one 7.7 mm and one 12.7 mm, or 2 12.7mm machineguns proved virtually worthless against Allied fighters.

On the matter of pilot training, this varies somewhat. The USAAC was a mixed bag of highly qualified pilots that originally were trained prewar and more hastily trained ones that were in expansion classes from about 1939 on and had fewer hours. The pre-war pilots often had several hundred to well over 1000 hours flying time and were generally very skilled. This is the sort of pilot that volunteered for the AVG for instance.
The newer pilots usually had just a couple hundred hours time mostly in training with limited operational experiance.
The USN both by the nature of their flying operations (carriers) and smaller service requirements generally had pilots of very high skill level who were comparable to the USAAC pre-war pilots. Many had close to or over 1000 hours flying time. They were also schooled in a set of tactics that were exceptionally good for the time.
The Japanese pilots were much like their USN and pre-war USAAF pilots; highly skilled with large numbers of hours flying operationally. Their tactics were somewhat unique and did not follow what had become standard practice in Europe. The Japanese fighter formation was a three ship flight following in a loose trailing formation staggered right and left. Tactics were much like early war RAF ones but the loose three formation gave much more room to maneuver than the tight "vic" that the RAF initially was using. Diving passes with a climb away from the target was a prefered method of attack.
The Commonwealth in the Pacific initially suffered from poor pilot training levels as well as equipment. Many of their pilots were hastily trained in the mass production system that Britain had set up early in the war to get alot of replacement pilots in the field.
Many of their pilots had very limited operational time on the aircraft they were flying. Most had barely 100 or so hours flying time in many cases having only recently completed flight training.