When i got my first decent mountain bike I thought I get extra street tires for road use. Well after 2 changes, that got really tiring so I figured I should get spare wheels and just swap wheels. Well that meant readjusting brakes & gears every time even though they had nearly identical rims & hubs.. So now I have a really good full suspension mountain bike with knobs for riding on gravel roads (real gravel roads in farm territory) and for single track. Another mountain bike with street tires for commuting. Another mountain bike with studs for riding on ice. Another mountain bike for touring with fenders and racks, front dyno hub, wb cage and street tires that can handle non-paved roads and bike trails. Four mountain bikes configured differently seems about right. I've owned about 25 mountain bikes and most got sold off. Any others I still have will be sold.
Newer mountain bikes with full suspension and a decent fork are pretty good for trail riding but just about anything will do for street. There are so many older mountain bikes available for less than a pair of tires that make excellent urban bikes.
There is no one perfect bike. I raced and ridden enough mountain bike courses to learn that each course is better on a different bike. One bike may be excellent on a particular course where another does quite badly. And you would be surprised at which does better. it's not price or reputation.
Spend the money on a good trail bike and don't leave it out side the local coffee shop. Get a 20 year old mtb for town and you won't get upset when it gets stolen.