Panther beat Stark because T'Challa joined the Avengers under the intent of watching them and making sure they weren't a threat to Wakanda. He has Stark's Iron Man schematics memorized--all he had to do was disrupt his force fields, then with his anti-metal claws, which made a total mess of Iron Man, he took out his oxygen gel packs (which go into his fuel mix, thus taking away flight, weapons and life support systems). He beat Iron Man because he had the upper hand.
Panther does have enhancements, but it's nothing that makes him stronger or faster than anyone could be outside of intense training. He is one of the best athletes and combatants on the earth, and would be regardless of the herbs.
Panther does train constantly, as he lives in a much more dangerous position than Batman. Batman chooses to do what he does. Panther was born to it and needs to be ready at a moment's notice. As far as his style--he threw the entire world economy into a free fall, with one phone call, just to spite an opponent. Wayne could never do that.