[Didymus]

White primer makes an enormous difference. It's another world compared to what you've attempted.

Seems like you were struggling to fully cover the gray primer by using multiple coats, thick coats and heavy, wet coats. It may be the photos, but it looks like you still haven't achieved full coverage; to be blunt, the yellow still looks drab. For your next attempt, white Tamiya primer is the obvious solution; it's much more opaque than regular paint, so you can use far fewer color coats.

In a nutshell, white primer should always be used under yellow, red, and all light colors.

I don't know about the opacity of Scale Finishes, but with PPG or Dupont Chromabase urethanes, I get a brilliant finish with just two color coats, even shooting white, pale yellow or a pastel tint.

Wet coats seem to have caused you problems. Once again, they aren't necessary if you've got white primer underneath. I use those automotive urethanes thinned 3:1 with medium temp reducer, and I've never had a problem with solvent "eating into the primer." (I buy both the basecoat and the reducer locally at Finishmasters, an automotive paint supply house. The basecoat costs $14 for 2 oz.)

Automotive urethanes flash in less than a minute, and are fully dry in less than ten. With paint that dries at that rate, I've never seen the need for a dehydrator.