Getting a smooth brush mark free surface using modern acrylic paint is tough at best. Yes, it all dries too fast. Here's some ideas that might help;
1- More Flotrol can be added than is recommended. Flotrol doesn't thin paint but it will lower the paints coverage, more coats will be needed.
2- Add a little water to the paint. It doesn't take much but a little splash in the paint your painter is using will help it flow out. This can be combined with the Flotrol for better results.
If you have to roll the doors there are some nice smooth surface rollers on the market.