As I read it everywhere, classes in the games I mentioned in the title differ in power a lot. This takes place in 3.5e and wasn't fixed in Pathfinder. Some search indicates that this problem isn't that strong in 5e anymore, but still present in 4e.
Were they created on purpose? Or was it a mistake?
Why was such an unbalance kept for so long? Why weren't the "weaker" classes buffed, or "stronger" classes nerfed? Were the class tiers created on purpose?