Looks like you could run some more current through the input stage. Try R2 at 10k or so and R4 at 1.5k for starters.
Yep, it looks like crap to me.
If you are looking for a simple mosfet design, I suggest just go to Pass Labs forum and study some circuits designed by Nelson Pass.
i did i built one of the zen amplifiers and it sounded great, all i need is just a big heatsink to cool it down, i also had some input issues but otherwise it was great
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i should just scrap this its basically a doodle i made.
I Have an whole series of posts dedicated to my attempt at undervolting the ZEN amplifier https://www.diyaudio.com/community/...s-amplifier-to-an-15-18v-supply.418925/page-2
Consider the no signal DC bias: the emitters of the input pair must be about +0.6V and the gate voltage on M2 is the same. The resulting source voltage implies many volts across R1, hence many amps. Gate voltage needs to be independently adjustable.