I don't consider the Canon depiction of rin as thicc. There's a lot of anime girls who are called thicc who are not. Mordred is another example of false thickness. Rikka, I'm not sure. Sonico is thicc. Not sure who else. Probably Nana from darling
I think the only thicc fate girls are Raikou, Scheherazade, Gorgon.
Rikka’s def Thicc. Pochaco is even thiccer then Sonico.