Slow or fast dry paints dictate the base coat type. The fast dry paints are Hot, and need a base coat that can withstand the solvents in them.
Promoter is just there to give a bonding surface for the paints. It's not a primer. Paints that are not "Hot" based, can be applied directly over the promoter, like rattle can acrylics made for plastics, or slow dry enamels. Acrylics are fast dry, but there are different base types of acrylics. This type can be very confusing because of that.
2k Urethane paints are hot, and need a base that can handle the solvent's, and why primer is suggested. Single stage paint uses either self etching, or epoxy primers, but is made for metal application normally. Primers can also be Hot, and need a surface that won't give to their solvents.
Random stuff to consider when spray painting....
The windows given are because they need to be re-coated before the previous coat has fully dried, and still has solvents in it. Once enough solvent has gassed out, it can be damaged by the next coat as the new solvent eats into it. Cure time and dwell time are also terms used. 2k paints can take 30 days to gas out fully, and is the cure time. Rule of thumb here is if you can smell it, it's still curing. "To the touch" term just means the top has skinned over, but underneath is still wet and still drying. Tacky means just that, it's sticky but doesn't lift and leave paint on your finger, and soft enough to leave a print mark.
Fun fact... Some paint's dry by osmosis. 2 part industrial epoxy, and lacquers dry this way. If applied during high humidity, the water vapor in the air will be sucked in as it out gasses, being trapped under the surface. This is called Blushing. Blushing leaves a white foggy appearance in lacquer coats, and a yellowing appearance in epoxy. Both can be fixed by applying a hot solvent approved for thinning the paint. It opens up the surface and as it dries, it pulls the water vapor out with it, and as the surface dries again, it seals it back up as the vapor exits. No more Blushing.