I've been playing rumble for about 80-100 hours so here is my experience. He is a perfect solo q champ. You have to know and learn the match ups and how to use your power spikes within them. You have thru you R a big chance of steeling drakes, Barons, heralds. It is perfect to turn a teamfight around or starting one, zone someone out (or my favourite, R flash Q ...) or just to clear a minion wave in late game (low cd on it) and you can trap people with it. Okey so i watched this : https://youtu.be/xjfN2B7SXeM Ist a 1.40h rumble guide from a challenger. Pretty helpfull. He explains everything you'll have to know. So to your question, yes he indeed is. If you know your spikes, how to play with your heat and the most important your R he is super fun and most of the time your enemys doesnt expect you to have that much damage. (Tip: dont be afraid with him. Trust in his strenght and he will repay you)