Giant Scale:

Well I think you got a bad batch . I just finished my cowl and wheel pants on a 30% extra. It came out beautiful, very smooth, nice color match.
I had a problem with 21st century paint much like you had with perfect.

I used sandable primer from an auto store. 400 wet sanded the primer. Shot first full coat, 600 wet sanded that then gave final coat, very nice looking. I always set the paint can in hot tap water to heat it up, regardless of which brand.

some of this paint sits on shelves for so long it is hard to shake it up. That was the problem I had with the 21st cent.