So essentially I'd like a light duty, slim tire mountain bike with road style handlebars.
Go find a hardtail.
Put a surly corner bar on it (or clone of)
Install skinny tires. Done.
I rode a hardtail 29er with 700x40 x'plor MSO tires. At high PSI and being an aluminum frame, roots could get jarring.
With a steel frame and tubeless gravel tires, which are now available in 45c and 50c. Ren herse has a 2.2 / 55mm. It would be a great gravel, rough trail bike.