It's not that I don't like her. It's more the fact she totally ruined her upward momentum of having increasingly better roles in the franchise. Especially after Skyward Sword, Breath of the Wild Impa was extremely underwhelming. The game had a huge Sheikah based theme, but Impa, the franchise's first and only real Sheik character at that point, was totally neglected and was just given the same old role as in the NES Zelda basically. If the roles of Impa where swapped between Skyward Sword and Breath of the Wild, Impa would be a newcomer now, and probably unique.
to be honest i think sakurai's bias is what's keep zelda characters out of smash