Technically, the Hemi head is superior to a wedge head, and a 4 valve head is really a hemi head, too. A hemi style head has the shortest path in and out of the cylinder and isn't hampered by having the valves shrouded by the cylinder wall. Typically a wedge head has twist to the port, and even when it doesn't, it is always going to be close to the cylinder bore.
Doesn't mean that a wedge head can't be made to perform but you have to work against some laws of physics to do it. Kind of like drag racing a FWD car, it can be done, but it requires extra effort to overcome some inherent disadvantages.
BTW, the traditional hemispherical combustion chamber is much less efficient than a wedge combustion chamber. So they both have their pluses and minuses.