I imagine that breaking DS spokes has something to do with leading vs trailing spokes. If I recall correctly, trailing spokes go slacker under torque. This means that if a big, strong person with a huge gear (which mountain bikes these days have) puts down serious torque, your DS trailing spokes, along with your NDS, would go slack. This in addition to local rim compression at the contact patch.

28 spokes seems to be the standard for even the lightest people. If you’re big and strong, 32 might not be enough. I’d look into 36. You’re restricted to J bend at that point, probably, but that shouldn’t be a big deal. I’d also probably go with beefier sapim Race/CX-sprint spokes. They’re stiffer so they’re less likely to go slack. I’d also go for the beefiest, deepest rim I can find to reduce local compression (at the risk of causing cracked rims, of course).