I agree on many things written here (but not all!).
I commute, climb mountains, do 5+ hours road trips with my roadie friends, ride sunday leisure rides with my wife as well as bike tourism now and then. Full suspension eMTB is remarkably good for all these activities and most comfortable "endurance road bike" I've ever ridden, even though that opinion is a heresy for traditionalists.
My thoughts on riding long distances:
- "Ergo grips" are no good, they allow only one good riding position, which is exactly something one should avoid on long endurance rides.
- I have found inner bar ends are a great solution. They enable multiple hand positions (similar to riding on hoods on a road bike) and allow avoiding "arms wide open" riding position.
https://www.bike24.com/1.php?content=8;product=192456;menu=1000,2,14
- Actively using the dropper post helps avoiding saddle sore. Drop the saddle on downhills, move your azz backwards and go low. Regularly changing your riding position helps a lot.
- Maybe get yourself another set of of wheels and tyres, one for commute and road/gravel riding, one for harder mtb stuff. E.g. Schwalbe G-One is fast and silky smooth for gravel and road riding. Tyre comfort is important for endurance (excepting the "harden the fu:k up" people of course).
- Personally I've found that Fabric Scoop Radius Gel is really comfy, but as said before, saddle is a highly personal choice.