I was discussing this last night with BC and we've come to the conclusion that grabs are what make the character roster so unbalanced or at least one of the biggest factors in character imbalance.
I mean think about it. All the high tiers except Rosalina (who has Luma) and Yoshi (dat air speed and shield pushing moves) get great rewards from their grab or have very easy to land grabs. Those with good grab rewards get kill throws or mostly guaranteed combos. Of course there are are low tiers with pretty good grab games (Ike and Mii Swordfight), but it doesn't make up for their other lesser qualities.
In another Smash game, this would have not been that big of a deal. However in Smash 4, shields are so strong (very low shield push/shield stun/shield poke) that grabs are pretty much necessary to break through. If you have a bad grab with a bad reward (Ganondorf, Villager, Samus, etc.), you have a major disadvantage.
I like variety in grabs and of course don't want every character to have great grab rewards or none. But seeing as how valuable grabs are in this game (again because shields are OP), it might be a good move in all honestly. Idk, grabs are just too necessary in this game, having so much variation in rewards/execution is inevitably a source of disbalance. Or just nerf shields.
And nerf rolling while we're at it.