In my opinion, I think it's fine without a hero limit - it's the way the game is designed. It's not a MOBA and it really gives a dynamic feel to the game in situations in which it works. Not to mention having more of the same hero on one team is more a disadvantage most of the time, than advantage. The freedom to have more of the same heroes on one team I think will really make Overwatch interesting, especially at an esports level. Every hero has a counter, so being dynamic in the game is one of it's best elements, sometimes the push might be to have a few of the same heroes and if it works, great, adds to the element of suprise.
Lots of MOBA players, who played League / DOTA 2 have the opinion that you shouldn't have more than one, or not changing at all (which is what the game is solely designed around)
Just my thoughts
![Smile :-) :-)](/styles/default/xenforo/vbSmilies/Normal/smile.gif)
of course not everyone will agree, and some will