well, as a e-bike rider, and as a cyclist from long times passed, honestly, there's no "magic solution" - a saddle that is perfectly comfortable for 70-80 miles on my road bike, brings me to tears in 30 miles on my cyclocross bike, and I doubt i'd get much past the end of my street with it fitted to the MTB. This is down to the difference in body positioning on the bike, and the different angle that the sit-bones come into contact with the saddle. Basically road > cross > mtb go from most horizontal to most vertical.
In my case i'm comfortable on a Fizik Arione on the roadbike, but it'd kill me on the other 2 bikes as it's much narrower and almost completely unpadded anywhere, with no real "give".
For the 'cross bike, it's a bit higher at the front end as the bars aren't "slammed" and also are a different profile - plus - on mixed roads, sustrans paths and bridleways you tend to ride on the tops of the bars much more. This basically moves my shoulders up and back maybe 2-3 inches, which in turn rotates my pelvis and means more of my sit bones in contact with the saddle - and to support that, I end up with a saddle with more "flare out" at the back - I think i'm running a old model Fizik antares on this bike - models probably changed by now, but it's the one that you're intended to sit "on but in one place", whereas the roadbike "Arione" is more of a "sit on but move fore and aft depending on if you're climbing or descending". It's quite similar, to the "Charge Spoon" saddle as a budget version.
Then we come to the e-Mtb - which, if I'm honest, really doesn't get used as a mountain bike, slammed down bike park trails and red/black runs, then use the e-bike motor as a winch to get to the top again - no, honestly, its used on same paths, bridleways, towpaths and around the woods that the 'cross bike is - only, it's used when the paths are boggier, and muddier, and claggier. But, it's again shorter than the 'cross bike, has flat bars instead of drops, that are wider, and all that makes it very much "sit up and beg" compared to the drop bar bikes - and as such, i'm way more comfortable on something that actually has a small degree of padding. I think at the moment I've got a ancient (as in probably pushing 20 years old) WTB saddle on there - it's about 1cm shorter and 1.5com wider than the Antares / Spoon and it's actually got a tiny amount of padding all-round.
BUT - here's the thing. I'm used to saddles with little or no padding. I can't get on with gel saddles, or squidgy ones, or ones with cutouts under your nuts (they invariably cause chafage, or just snap at the middle point of the saddle as i'm a fat sod). And, the saddles I choose aren't a static thing... I've a box with about 20 saddles in it, various makes and models - because about 16 years ago, I went from weighing nearly 30 stone, down to 17st. and as I lost weight, the saddle that suited me changed. Each saddle has a note stuffed under the frame rails, detailing what it was used for, what weight I was, and when It went "inappropriate" and was pensioned off. I've saddles from Fizik, Selle Italia, Selle Royale, Specialized, WTB, and others - I've none in the box from Brooks because - well - I kind of fell out of love with them in my early 20's when my Brooks Team Pro (the skinny one with the massive copper rivets) got soaked during a 12 hour TT and was like a hammock by the end of the ride. Was basically un-salvageable apart from sending back to brooks for a new leather topping, which after postage was about 20p less than buying a new one. But I digress.
What I'm trying to say is that i've been riding bikes regularly from the age of 12-13, seriously from 16 till maybe 30, and then intermittently for the next 30+ years. That half century has been a un-ending and unrequited search for the perfect saddle. and for My Arse, there isn't one. Some people are capable of riding on anything - others couldn't get comfortable on a saddle that was 3d printed from a scan of their nether regions, then heat moulded to their form in-situ while riding.
The Biggest mistake people make with saddles is thinking "it'll break in to my backside" if it's a Brooks leather saddle - or "my backside will get used to it" if its any other make or model.
IT'S NOT YOUR BACKSIDE THAT GETS USED TO IT. IT'S THAT YOU'VE RIDDEN ENOUGH THAT YOUR LEGS ARE STRONGER THAN THEY WERE, AND ARE BEARING THE WEIGHT THAT ORIGINALLY WAS BEING PUT THROUGH YOUR "CONTACT POINTS" - it's the same reason your shoulders and hands ache when you return to riding the bike - you're using bits that aren't normally weight bearing items to help support your body weight.
There's lots of theories abound - I personally tend to subscribe to the "get your sit-bones measured" then take advice on what saddle is the right width for the bones, bearing in mind also the nature of how you're body is positioned on the bike.