Well our arena is about fighting A.I, so I think I don't need to argue any longer about that issue.
Anyway WL and MB is not as high, but yes it's viable with the addition of one GS/GR. Some ppl already tried and success while you keep complaining. With the class restriction archer can still be used. Albeit in a different way.
And some other games also have that kind of restriction with more limited amout of units viable for arena. So i think why not for VF, as we got more variations of viable arena units.