It dampens the competitive scene not to have access to all the characters. It's difficult to join a team and play support if you don't have access to the support character you need to play. And since the most recent Dota world champion was 16 years old at the time, kids matter. And kids can't purchase the characters they need to purchase, since they have no money.
There's a thriving competitive scene in both games, so maybe the effect isn't so bad in practice. But if you want to play soccer, you'd find it difficult if you didn't have access to certain parts of the field unless you pay money. That seems like an accurate description of League's model.
The central issue is this: If you want to follow the strategy of making a new game competitive and then funding a yearly tournament, your game is more likely to fail if it uses League-style "pay for access to the competitive landscape."
League works for League. It's largely thanks to history and timing that League grew to such a degree: When League launched, there was no Dota 2 and no HoN to compete with them. League's model is less likely to be replicable to a new game.