Incidentally right now I've got a "sport" mountain bike for sale, a bike I've had since 2002 and has served me well. But after having a dedicated commuter bike for a few years and now a dedicated mountain bike, it's easy to see its shortcomings at both. I now have both the wherewithal and the room to have both (and a tandem, and a C&V, and other family members' bikes).

As a road bike, if you put 1.5" slicks on it, its gearing comes out wrong, and it's not efficient. Better to have a lighter bike that puts you in a position to make steady power. But it takes a rack and luggage like a champ.

As a mountain bike, the biggest problem is the fork isn't up to snuff. Its seating is much like any modern hybrid, but mountain bikes are now sitting up and back a lot more with wider handlebars and more raked-out steering. And rear suspension is now good enough that there's no really great reason to avoid it. It isn't tubeless-ready and it doesn't have thru-axles which IMO are great. The max tire is 2.2.