I never said bruisers are immune to Zoe. Her biggest counters are bruisers because they have the easiest time dodging the ability, (most have fair mobility) usually have counters to her abilities (Fiora's Parry, Garen's Courage, etc.), have enough damage to punish her for mistakes, have enough tankiness to survive a blow (unlike ADCs and supports, who are clearly the main complainers), and,
most importantly of all.
They have the correct natural positioning that counters Zoe.
They stick very close to Zoe to deal their damage. Zoe doesn't like that. She doesn't even deal a lot of damage at that range. She, like Aurelion Sol, likes her targets to be at a fixed medium or fixed long distance. And like Aurelion Sol she has basically only 1 ability to help her actually peel except (her E), maybe her W if she gets lucky. So if she misses her E or it gets blocked (very likely vs. bruisers), she is done for in a 1v1, and even if she hits it, she doesn't really win.
Keep in mind she is mainly a 1v1 champion. Losing at her own game? Boom. Hard countered.
Seriously. Try playing
vs. her. It is hilariously easy, especially if you are a [listed champ] main.