I was actually thinking about Jigglypuff and reflecting on the idea that "undertuned" is the perfect word to describe it.
Consider the following:
-Jigglypuff is an aerial-based character: the floatiest character in the game, multiple jumps, 2nd highest air speed, etc.
-Because Jigglypuff is in the air more often than not, and because it lacks a command grab, this means it can't threaten shield the way most characters can.
-Also, Jigglypuff is bad at tomahawking due to said floatiness
-But Jigglypuff has a move that does a lot of shield damage: Pound. So ideally, if the opponent isn't shielding, you space aerials. If the opponent IS shielding, you use Pound.
-...Except Pound doesn't do quiiiite enough shield damage to regularly break them, and it has huge endlag that's punishable. So, people aren't forced out of shield as often as Jigglypuff would like.
There are a few other odd quirks of the character worth noting, like having really solid traction that allows it to land grabs that other characters wouldn't...except Jigglypuff also has tiny, tiny arms, which makes grabs difficult in the first place.
If patches were possible, more shield damage on key attacks might do the trick. Without them, though, the main angle of development I see possible is getting better at understanding when the opponent does and does not want to shield and wearing them down accordingly.