I'm not sure what you mean by that? You can either use the ASI to get one of those abilities to its pre-capstone max of 20, and then the capstone takes it to 24, or you use the ASI to get a feat.
If you were to use the ASI at lvl 19 on STR or Con to reach the increased cap of 22 then once you hit lvl 20 the ASI has been wasted since Primal Champion only raises the cap to 24.
Ideally Primal Champion would simply increase by +4 and set the cap to 30
Ah, I missed the fact that the lvl19 ASI specifically is allowed to break the max of 20. Yeah, that's a weird interaction. They just need to change it so that it increases both your score and your maximum by +4.
I don't think what you said would make it work with Giant belts though, they just set your strength to be that number, you're not supposed to be able to boost beyond that number.