FWIW, when I do longer, more serious rides, I use BOTH AllTrails and MTB Project. When riding near the limit of my range, I typically do a trial fun first; if there's a lot of ascent, I often don't make it the first try anyway.
To figure range, I look at the total vertical climb that's involved and the total mileage-- I know the 46 pound eMTB can get a bit over 40 miles with 4,000 feet of vertical -- but then I also look at the grade. If there are a lot of long stretches of 10 or 15%, or short stretches over 15%, I will figure my real-world range will be a bit less.
For choosing trails, it's tricky-- I'm looking at one ride now where I'm really not sure how tricky the descent will be on the gravel bike. I'm always thinking of bug-out routes; there's one route through the Verdugos that I'm pretty sure is gonna be fine, but surface conditions are a big factor (and I've had a recent medical problem, so I'm not going soon anyway.) The biggest, and most dangerous, variable are some very steep, sandy segments where I can just barely go up, but might not be safe to descend. So far, using AllTrails and MTB project, I've been able to flag those segments and avoid them.
Sorry about the survey, I just saw this. I have a blanket rule of not taking any surveys or providing any feedback that can be converted into data or metrics. I just don't like providing data if I don't know EXACTLY how it's being used-- a bit extreme, I know! I do call supervisors to praise great customer service, but never provide ratings. Very hypocritical-- in grad school, I had to collect data for plenty of projects! Good luck with it.