Guys remember that one time Evil Geniuses won it for NA in Dota 2? /cries
DOTA is so weird though. Egos don't ruin teams as much cause there's a lot of individual decision making. So you can make these all-star teams with huge egos and sometimes they work (EG TI5) and sometimes they crash and burn (Secret TI5). Also DOTA is just a much more volatile game so its a lot more likely that lower tier teams can pull an upset or get hot and go on a streak.
I bet if u took the top 1 or 2 players from NA and EU at their spots and actually put them on the same team they'd be alright. Caffeine, Fan, Zuna, MC, Mene, Bakery, etc. all in one place could do some damage. I realize 3 of those players were on Naventic at one point but Kenma being bad, aforementioned ego problems and their lack of a tank forcing people out of position ruined that.
I think if you did that kind of EU/NA combo stuff in HOTS like what EG is now in DOTA (zai/Cr1t- are EU) the west would have a chance. I think it will happen eventually but the scene just needs to evolve and mature for a few more years before we start to see it. It didn't happen in DOTA until the past two years or so.