As for Cait though, I don't have that ability (I don't think anyone else did, I am guessing thats not implemented in the steam version), even so, its the gear that's basically giving the 22 point difference?
Cait's new gear change isn't in the Steam version yet but Ryn and Brint (not Brienne) both have gear changes available in the current public version.
And yes, it's probably Cait's gear. Companions
do have actual items that are equipped and their Gear that's displayed at the bottom of the equipped item list is basically an abstraction of their equipment, their Power list and their stat balancing. The equipment descriptions/stats aren't actually
visible in-game but some of the stats can be seen in design docs. It's quite possible that Cait's gear tweaks her Spellpower such that hers is higher than Kiyoko's.
As for why Kiyoko's stats don't change when you swap her Gear, it might be because she was the first companion to have gear changes and hers were all built-in from the start. Or it could be that Tobs just didn't feel like rebalancing her stats for each set, liked how she was as-is and decided that all she needed was different slates of powers.