That's a 6th level PC that is very versatile with 4 At Wills, 2 level 1 encounter attack powers, 2 level 1 daily attack powers, 2 level 2 utility daily powers, and 2 level 3 encounter attack powers.
But, the PC can only use one of these at a time.
Can you clarify what it is that the PC can only use one of at a time? For example, can the PC use all four encounter powers?
(the At Wills add versatility, not power).
This may be true in some cases, but it is easily disproven. Many at-wills gained will result in a more powerful character because they will have a better option in different circumstances. A paladin who picks up warlock at-wills, a rogue who picks up twin-strike, a fighter with righteous brand, etc.
He can mark with Combat Challenge or Divine Challenge, but not both at the same time.
Does anything stop him from making with divine challenge and inflicting divine challenge damage _and_ making an immediate basic attack if the marked target attacks someone else?
At level 11, he cannot take a PrC class and gain 11th level PrC powers. He has to minimally wait until level 14.
Does he get access to paragon feats at 11th and get +1 to all his stats? Does the needing to wait matter that much to someone who is already 14th, if you're making a game at that level? As a note, the general principle of 'sucks now to be overpowered later' is generally not desirable, no matter how much grandfathering it may have in D&D
There are not just advantages here, there are also restrictions here. Yes, the PC is extremely versatile. But, overpowered? And what about higher levels when other PCs each have a 15 level Daily Attack power and his highest level Daily Attack power is 9th level (highest level Utility power is 10th level)?
Is being slightly worse in one combat per day (when their high level daily is used) reasonable recompense for being better in every other combat?
Were 3.5 Fighter 6 / Wizard 3 PCs more powerful than Fighter 9 or Wizard 9 PCs?
Not usually.
Isn't the concept similar?
Similar, but 4E classes are not designed the same way as 3e classes and even then the 3e comparison was more like 'Is a fighter 4 / barbarian 2 / ranger 2 / warblade 1 better than a fighter 9' and the answer is overwhelmingly yes.
He finds it to be not multi-classing. Gaining a skill and a once per day ability does not make one a Cleric.
True, but is it overpowered for the use of a feat? Would more feats to get more powers be unbalanced? I think allowing the at-will like PS does is a big change there too.
At any rate, the actual way to do merges of classes in 4e is to design a new class. Ex: Swordmage. Anything else is mostly a trap, one way or another. A rogue who is 3 levels behind who gets hunter's quarry, fox's cunning, disruptive strike, split the tree, twin strike, nimble strike, and toughness or defensive mobility instead of whatever he's getting for the missing 3 levels is almost always better, except for a couple levels apparently where he gets nothing at all for the multiclassing (which seems odd too)
