Sold my MTB as I got bored riding the limited bridleways near my house, and I some stupid principled objection to putting the bike in the car and driving for an hour to have a bike ride. Bought a CX bike instead that’s enough for light off-road work and with road wheels and tyres makes a decent winter training bike. Until the quite recently MTBs could reasonably be ridden for a few miles on the road to reach trails but today’s MTBs don’t look like that to me, gearing good for a max of 10-15 mph?
One of the main reasons I stopped MTBing a few years ago. I too bought a CX bike but found it too much of a compromise on the local trails so it just ended up being a slow road bike. A decent EMTB however handles rough terrain with comfort and ease, but can also power along the tarmac. The lanes around where I live are in a shocking state and really no fun on a road bike anyway. Mine has been chipped to remove the 15mph restriction but the reality is that with MTB gearing, huge tyres and a 21kg weight penalty 20 mph on the flat is about the sweet spot. I can now go further, in more comfort, without feeling like I'm wading through treacle on the road and have fun!! If you want more of a workout just reduce the power assist. On the road I rarely go above eco on the flat and tour will get me up most hills. The biggest cost is in money, which as they say, you can't take it with you when you go!!