IMO Paint dulling/fading/sand scratches appearing etc. after completing all goes back to body work/primers used.
Im old shool used to use laquer based everything back in the 80's. Used to use Enamel clear over laquer to minimise dulling.Even the the catalysts in the single stage enamels were almost guaranteed to dull out and require sand/ buffing.
Things are different now. I only use epoxy primers on initial main body work filling and blocksanding. You then can use a simple sealer with usually no worries.
Wish I had that back then.........
Base coat clear coat simplest to use. A monkey could paint it. (except metallic colors),As long as the bodywork is passable at the least. Old saying goes, finished paint is only as good as the bodywork prep.....
Dave