This year Worlds has the lowest champion diversity
Season Champ contested Champs available Contested rate 1 -------------------------46 ------------------------- 76 -------------------------61% 2 -------------------------59 -------------------------102 -------------------------58% 3 -------------------------69 -------------------------115 -------------------------60% 4 -------------------------61 -------------------------120 -------------------------51% 5 -------------------------74 -------------------------126 -------------------------59% 6 -------------------------56 -------------------------132 -------------------------42%
Thx Rito and their meta Source: https://www.reddit.com/r/leagueoflegends/comments/595tda/worlds_had_highest_champion_diversity_last_year/
Meanwhile in DOTA 2: 103 / 111 heroes were ban/pick in TI6 http://i.imgur.com/7SZE95h.png
Edit: Highlight comment
You can have 90% champions picked in League as well, but the cost would be the total destruction of low elo soloQ balance.
Dota balances for competitive play first and foremost. If that results in something being busted at low elo, well, bummer. Better stop being bad and climb out of low elo then.
Consider picks like Amumu or Volibear, which are not viable at the competitive level because they have very exploitable weaknesses (weak early game/extremely kitable respectively), but are still very strong at low elo. Then imagine Riot buffed those champions to the point where they were viable competitively. Now those champions would be absolutely fucking broken at low elo with 60%+ win rates.
That's what Dota does. And when people say "but Omniknight is so OP it's unfair" the response is just "get gud".
I'm not saying that's a better or worse approach, but you have to understand Valve and Riot have fundamentally different balance philosophies. Valve balances for competitive, at the expense of some champions being busted for most players, while Riot balances for the majority at the expense of lower champion diversity in competitive play. Just the way it is.
Also the pick/ban structure is different in Dota, and there are champions that are legitimate hard counters to others (which doesn't really exist in league, and can't because not all champions are free). It's just a different game, apples to oranges.