You only played for 2 days. So have I, actually. I have come to completely different conclusions.
Tanks have the lowest skillcap. It's not hard popping barrier as Reinhardt and covering your team or pushing the objective, slamming someone into the wall if you see an opportunity. They most certainly don't one-shot people unless said people fuck up utterly.
It's very easy popping a Hanzo ult into a contested capture point against people who have no idea what they're doing or what Hanzo's ult does. That doesn;t make it OP or effortless,it just means people have to learn avoiding it. Same goes for pretty much every other ult in the game. They can all be avoided in a very simple way. If you don't, this means you've made a mistake. Can't blame that on lack of balance, but on your lack of experience.
I'm sure there are some unbalanced heroes, but there are no clearly OP or useless heroes. I'm sure some balancing is needed, but OW definitely doesn't need "serious balancing" and it definitely will not bomb.