I agree that you have more control by just using the alpha from keylight, and then correcting the source by hand. Auto-spill supression in all the major keyers (primatte, keylight, sometimes even ultimatte) can be clumsy. If you need to make a stack like that, and even double it and find edges and blur a second track matte to do some edge correction, it’s probably a more versatile workflow.
HOWEVER, all I’m saying is simply that you can turn off keylight’s hyperactive spill supression by setting screen matte to source. Then you have the option to use the color correction tools in keylight or otherwise.
Also, I agree, ultimatte is the best.
😉