My wife had one on her mtn bike and after two knee surgeries is thinking about getting one one her ebike. She has a Gazelle Arroyo with a step through frame. As for "laying it down" some people don't have that level of mobility. And as to serious mtn bikes don't have droppers, you can't be serious. I ride my old CX bike for gravel rides but if I was getting a new gravel bike for where I ride, I'd get one with a dropper and some type of front suspension. If you're getting a dropper, study them carefully. You can spend a modest amount with a cable and spring actuation or fully electronic for a small fortune. At the end of the day, go ahead and get any bike with any modifications that will get you out and enjoy riding.