You cant become overpowered in the right hands, that would mean the champion is in fact imbalanced. Balance should be done by seeing what high skilled players can do with a champion. If a newbie cant handle the champion or infact owns a game full of lvl 1s it doesnt mean anything in any way.
Vlad starts out sorta slow as his drain is on to long a cooldown at the start, but as he gains lvls and ap/hp he can top off his hp quite easely. He's also harder to kill then quite alot of mages because of the higher hp treshhold and good escape ability. Might say that hp wont help him without defense, but it helps more then not having it anyway
Overal not overpowered in my eyes, quite a bother in the right hands, but unless fed i havent really seen a vlad dominate hard yet