No experience here with either bike, so take this for whatever it's worth.
First, I have to smile when I read something like "I wouldn't ride a bike that can't take a size X tire." To some extent, I think tires are like gears. Just like there's always a route too steep to ride with some gearing, there's always going to be a route with rocks too big to comfortably ride with some size tire. (Though, to be honest, I'd probably be hiking instead of biking a trail where 3" tires were too small.)
I really think OP may be looking at two different bikes. You'd be hauling a lot of extra weight in the wheels to take a fat bike cross country (although I'm sure people have tried, and perhaps even succeeded). And while I'd prefer something in the 30-40 mm tire size to go cross country, I've found gravel roads and sandy roads that 38s couldn't handle gracefully. So perhaps you want to think about a cross country bike AND a gravel bike. Start by buying the bike you'll ride most near home, and ride it a lot. Check in with a local bike club or bike shop to find out what gravel is close by, and what you need to ride it comfortably, if that's your choice. Bicycle commuting is kind of similar to touring, except with a lighter load, if there's not some good gravel close by.
FWIW, if you've got to drive 5 hours each way to get to gravel or MTB trails, so you'll only end up riding every other weekend in the summer, that does not meet my definition of "ride it a lot."