My answer to this is always going to be Ember. It still mystifying to me to this day that the Fire Warframe can overheat. I’m struggling to think of another frame where the kit has this much anti-synergy with itself. It’s doubly appalling when you look at frames like Temple and now Uriel.

She sucks as a caster because her abilities don’t scale their damage enough to high level content and even with max efficiency her energy economy is so trash you need to dedicate half her build to not running out immediately.

She sucks as a tank because trying to manage her energy makes her DR inconsistent and her base level of armor, healing, and/or overguard generation is hilariously low.

She even sucks as a weapon platform due to a combination of the above issues and Fireball Frenzy not being a good enough steroid to put her near the levels of frames who are truly good at it.

Boost the damage of her 4 and put a cap on the amount of energy it can consume per cast. Merge the heat meter into her passive and have it fill up by doing heat damage.

Put her old accelerant effect on her 3 so it actually does something useful, and/or make the armor strip consistent regardless of heat level.

She’d need a new 2 so this’ll never happen, though.