When it comes down to ''feeling'' Theoden's performance in the mod, you could definetely say that he is underperforming, and that his health in his early levels is under-performing quite heavily. Especially when he is before level 4-5.
Unfortunately, I have trouble seeing a middle ground. The 3 PP spell may seem far away, but it can hit at the same as a Nazgul if you save up for it, and Theoden poops on Nazgul, doesn't he?
I think Theoden's early game, especially for a hero that costs so much to revive (2800 without any real mass slayer abilities!) is lackluster. A health buff might be worth testing, or some armour buff, or better scaling, it's a little tough to say for that matter, unfortunately. Do you guys think a health buff would be sufficient?