Essentially everybody below four stars (and a lot of four stars still, like MP5).

Due to how GFL works mechanically, there are a lot of T-Dolls that are amazingly cute (coughMP40cough) but dont make a lot of sense to develop past a certain strength point. Fate Grand/Order, despite its p2w ridiculous gacha flaws, at least balanced lower rarity cards with good abilities, while top rarity cards are often locked into certain niche uses despite good raw stats (to the point that 4star rarity cards actally hold the middleground of excellent utility for their raw stats).

It's hard to justify giving T-Dolls that aren't in your top fighter echelons a nice comfy space in the Dorms (unless you whale or are extremely patient to save Gems) too.