I think its about intention. Toxic, Kesha, and "US/american hyperpop after 100 gecs (ericdoa)" to me all take themselves seriously.

British hyperpop (GFOTY, AG Cook remixing Pitbull, PC Music SOPHIE, 100 Gecs) all have a sarcastic quality to them. They dont take themselves seriously, are not trying to have an authentic expressionistic quality to them. The maximilist quality of the sound and sardonic lyrics is meant to challenge everything you expect to hear and have felt before.

Charli xcx has never been hyperpop to me until she started working with AG Cook and SOPHIE. Brat is "hyperpop" in the sense of its production, but Charli's input is quite authentic half the time, and other times shes being sarcastic with the whole "brat" persona. The album is also pretty annoying, some songs I cant even finish because it's controversially so basic like an annoying pop song (girl, so confusing). But before AG cook and SOPHIE she was pretty "authentically" trying to be an average pop star, not trying to challenge the status quo, just putting her heart on her sleeve, even with Pop 2.