Bob's right about the hot water delay, it is longer in my masterbath. There is a garden tub and I turn that on hot for a minute before I shower. But it's a waste of water.
Pex is really designed with the professional plumber in mind. It's the fastest to install in new work with a minimum of on hand parts. A pro can do a new house in a fraction of the time it took to do copper. Plus pex pipe can adapt to poorly drilled and misaligned holes better as well. If you go pex you probably should just buy a crimper. They are cheaper online and you can find them with exchangable heads.
There really is nothing wrong with cpvc. It's been around a while.
I agree, it sounds like your valve has built in restriction. You may be able to disassemble it and get more thru flow by enlarging openings. I've done that on valves and shower heads.