Your conditions don’t sound like a simulation of a 300 lb rider with disc brakes,
cubewheels, they sound like the experience of someone who seems unable/unwilling to pick a line and lacks bike handling skills. I’ve been riding on 24h wheelsets on all sorts of surfaces, including some gnarly gravel and single-track for more than 5 years, while weighing a steady 78-80kg. I’ve broken exactly 2 spokes, both on pavement, and both while riding in straight lines while not braking, on front and one rear. I have no doubt that your country has some “interesting” roads, but yours isn’t the only one. We’ve got them here in Europe, and we have them in the US, especially in many of the rural areas.
For the OP’s stated use (and frankly any kind of smooth gravel): 32h might be good insurance, 36h is overkill (unless touring or exceptionally heavy), 28h is probably optimal, and 24h is definitely not a mistake. Assuming non-extreme examples like roads that aren’t roads and riders unable to pick a line to avoid direct strikes with “potholes”, the real factor in wheel durability is how well built the wheel is, not a magical spoke number.