A trail bike, an enduro bike, a downhill bike, a gravity bike, a cross country, a cyclocross, a hard tail, a rigid just in case, a fat bike, a hard tail fat bike, a full sus fat bike. Plus for the road a race bike, an endurance, a touring, something for gravel, a tri bike, a time trial bike (though I guess you could combine the two if you aren't at a UCI event), a fixed gear or single speed, a track bike (and a track), a few different road bikes with discs, maybe an S+S coupled road bike or touring bike or both plus a vintage road bike or 5 is handy. So yes I would fully agree only mountain and road, keep it simple ; )