Sounds like you want a dirtbike. For 10k you can go buy a Stealth Bomber. Full throttle, 10,000w full suspension. Everything your looking for.
It doesn't sound like that to be... what is a dirt bike? I thought they are ICE bikes with 80cc+ displacement, not a 1hp electric bike.
Are not all the Mountain Haibike, 350W Bosch systems being ridden on dirt trails? Does that make them dirt bikes?
If you have even ridden an Optibike mid drive, it is not made to be ridden on throttle alone. Why? The MBB spins at 2400 rpms and gets stepped down (like 30:1) to the chainring, 85-90 rpm. It can run down to 70 rpms under load, but it does not like it, it wants pedal assist.
the MBB mid drive is smaller in profile than a hub motor and spins about 10X faster. It tends to be more efficient, but within a smaller operating band. While the ddhub will perform from 0-350 rpms, the Opti MBB always wants to operate around 85 rpms and have you change gears. Thus, legs are needed between gear shifting and overall ride performance.
It is more satisfying to ride all MDs like a bike, as designed, and get the thrill of faster assisted mtn biking, than just throttle and change of gears.
If that's the case, then he's not looking for a zero pedal dirtbike.