Back in the day when you had a choice of lucite laquer, Duluxe synthetic enamal, or Centari Acrylic enamel we painted everything without clear. Laquer we would pile on sometimes 20 coats of product wet sanding after every half dozen coats. Tons of work but you could really product a beautiful finish.

Oh we had something like clear. It wasn't very clear even in the can and it yellowed in about a year.
Duluxe was like painting with rubber cement. Very sticky for many hours after the car was sprayed. This allowed the paint to flow out very flat with an average gloss. Very unrepairable and forget about buffing anything other that maybe a small dust spec. Then don't even think about it for at least 90 days. No clear coats just paint.
Centari was a production finish. No clear coats and no hardner when it was first released. Faster flash over that Duluxe. Dry to the touch in 3-4 hours but not hard under the flash off for 30 days. After 30 you could sand and buff but the shine was never the same as when sprayed out of the gun. I had a friend that owned a shop. He would run his Centari jobs through the car wash with the beater brushes so the new paint would match the old paint better. No clears until Centari 2000 which was a clear you added to the last few color coats if I remember right..

I used to have my paint store add balancer and binder to Centari mixing clear which was no more than a filler to give the paint volume. It was purple when you looked at it in a gallon can. I would add hardner to it and top coat metalic paint jobs and add pearl paste to it and spray it out over color coats for a custom finish. Compared to todays standards it sucked.
Fast forward through a whirlwind of revolutionary paint products that were cast upon the industry and marketed as the best thing since sliced bread. Some of them damn near put some shops out of business when they started to fail in volume. Anyone remember Cronar?
Well to end this painting history lesson... The best thing to come out of progress and time is the clear coat. I like two stage metalic colors but I am old school single stage when it comes to solids. Urethane sands and buffs the next days and achives a beautiful deep gloss. That's my 2 cents.