The "LoL" approach is somewhat incorrect. something like 95% of LoL champions are good, and I think 100% have a dedicated player that are in the highest tier of the ladder. The image of a smaller "good" pool comes from pro games playing so safe - in a lot of cases players will get skilled at a champ so they can pick it away from enemy players who are known for being good at that champ, not because of the champ itself. If the ban number was higher I think you'd see a lot more diversity but as it is well over half (I think closer to 80% but I forget the number) of the champs saw play in the official LCS matches last season, and the variety appears even higher going into this next season.
My point with all that is: Blizzard is not known for stable balance in anything except Starcraft and Starcraft alone. Applying their WoW class balancing habits to HoS, with the heavily gated hero access, is just asking for disillusionment. Again, I think they are really missing part of the appeal of the game by making it so hard to play different heroes that you want to play. The smaller hero pool just makes it seem more like it should be Smash Bros: Blizzard edition, not less. Maybe X hero from Y game isn't great but if I like that hero and just feel like playing them on a whim it's either $8 or a few weeks of casual play. Not very whimsical at all, in fact.