Keep in mind that fat bikes and mtb style bikes tend to have a longer top tube and reach than something like a road bike. This is essentially what differentiates it from something like a road bike. In reality it's just compensation for the difference between road and singletrack style riding. Mountain bikes encourage a different sort of position designed to be more stretched out and weigh the front axle as needed in rougher terrain. It's obviously not idea for road or even basic gravel use.
As for heavy riders, paat 220lb, it becomes much easier to bend axles, wheels etc. If you ride on smooth terrain, not a problem. If you fit well on your bike and know how to balance your weight properly, also not a problem.