Well, what exactly would these do? Add more power to their 4 skills? I think summoner masteries are just fine, and personal talent trees would be going overboard.
But as for that guy saying it'd make the game a grindfest, I lol'd, because, like, it already is one, so that argument is invalid!
Oh, I can easily play the 10 free heroes every week without any damn grinding. If I have a couple of favourites I can easily buy them. But what the OP suggests is
(Grinding ^ Grinding), which is why it sucks. Why does it suck more than what is already there? It basically makes me Grind the **** of one or two characters, which is no different than WoW. Right now this game is diverse enough/better.