Rear ballast is necessary regardless, no? If so, then the arguments about the rear hoe is pointless in a 2WD vs 4WD discussion.
The skinny front tire argument can be remedied easily by going to R4s on the front, and might be the wise choice, if you plan alot of loader work with your 2WD machine.
Terrain can make a big difference, but if you have challenging terrain, then even pulling a rotary cutter can be a problem with 2WD.
In my experiecne, 2WD tractors can do alot of good, fast, loader work... of course all things are relative, and ther are conditions where 4WD would be better... but certainly, 4WD is far from necessary all the time.