HotS is heavily built around the idea of champions being hard counter to other champions. HotS can get away with it because its laning phase is very non-traditional. It's rare to have two solo laners, which means being in a group of four is common. This allows teammates to cover your weaknesses and allow you to play to your strengths. It's also rare to be in the lane for an extended period of time due to the more objective-focused nature of HotS. It's also harder to snowball in HotS. There are more things to say, but I'll leave it at that.
In League, champions have to be able to survive 1v1 or 2v2 for many minutes. Any lead that one side gets can snowball easily without any recourse for the losing lane/team.
And as a side note, Biotic Grenade is an awful design, regardless of the fact that that kind of stuff is more reasonable in HotS.