I’m into all things two-wheeled, have done lots of road & mountain biking on bicycles, and road & dirt motorcycling. I’ll share my perspective, and apologize in advance for the length. I wouldn’t put them on a single 1D spectrum and presume to call one better than another, for me they all serve rather different functions. I’d completely agree with the advantages you list for road bikes, I just think there are other different advantages for mountain bikes, dirt bikes (off-road motorcycles), and road motorcycles.
Road motorcycling, especially if you can fix anything on the motorcycle, comes with a strong sense of freedom compared to car driving, and it’s for traveling longer distances. There’s an aspect of shedding all your dependencies, not needing to rely on a huge machine that you can’t fix, but still being able to go fast & far. Weird analogy, but I find it similar to long distance running - there’s a threshold for me above about 15 or 20 miles where it suddenly starts to feel like I can go anywhere with my feet.
Dirt biking is technical motorcycling, shares some aspects of downhill mountain biking, but requires a lot of very different skills from any other kind of riding. Learning those skills is really fun, and being able to get far out into the wilderness and access places you can’t go by any other means is also very fun. The technical riding requires a lot more simultaneous clutch, brake, and throttle work than road riding, and I find it similar in certain ways to playing the drums in the sense that you need a lot of body awareness and the ability to do things with hands and feet at the same time. Technical uphill riding is very different from downhill and/or mountain biking. BTW technical dirt biking can be insane amounts of exercise. Some dirt moto rides I’ve done are equivalent to doing 50-100 miles with big climbs on a bicycle, everyone in the group burned thousands of calories and started bonking by the end. Can’t talk while you ride, but it’s very social; riding with others is an absolute must, there’s planning beforehand, there’s lots of stoping and talking, and you can end up with a lot of camaraderie when working through difficult features and pushing your abilities or helping others.
Mountain biking has all the advantages you mentioned for cycling, it can quiet and serene. Even better than road biking sometimes since you don’t have to deal with traffic. I usually ride with others, but sometimes alone is very zen. There’s anything from riding dirt roads, to cross-country single track through the forest, to adrenaline: technical downhill or mountain bike park with jumps. Fabulous exercise, and a great way to experience the outdoors.
For the maintenance question, I’d say I probably spend as much or more time on bicycle maintenance, but it’s mainly because I currently ride bicycles much more frequently. The maintenance tasks are smaller, shorter, and simpler, but need doing more often. Cleaning, chain & joint lube, and fixing flats is the majority of bicycle maintenance. I bled my mountain bike brakes once, and that was pretty involved for a noob, required a special kit & a couple hours. The moto maintenance tasks take longer per session, they’re more difficult, and require more tools and knowledge, but they’ve been less frequent. Changing oil, bleeding shocks, fixing electrical, replacing parts. A tire/tube change on a bicycle is a 5 minute task, while a tire change on a motorcycle can easily take an hour or two if you try to do it yourself with tire irons (not recommended!). The big stuff goes to a professional mechanic, of course.