Months? What milage are you doing on tarmac? I used to commute on my MTB everyday to college and Uni, becuase it was the only bike I had. It still took a year to wear tyres with a decently hard compound out. I just used to run Fire XCs, fairly hard, fairly cheap, fairly OK off road, wearing the middle out just used to bring the shoulders into play a bit more off road, which was actually a good thing.
Get a supercheap hack for road work? Or is it all wear induced by road hacking to the trails? Def experiment with tyre compounds, I've had 'DTC' tyres that've worn out in seconds. Otherwise I find highrollers actually benefit from wearing in a fair bit, and the 70a is pretty darn hard. Thin hard run tyres like 1.5 conti XCs run at 50-60psi are pretty compromised off road unless you're riding in deep slop.
I don't think pressures are going to help at all, MTB rims simply can't take the kind of pressure needed to keep the carcass round. Get narrower rims to keep the carcase more round? that can compromise performance off road too though.