Elevation figures from sites are always wrong, in a way or another. To measure it accurately, one should ride the course with a decent altimeter, possibly on a day with constant barometric pressure.
That's not always practical. An elevation figure estimated from topographic maps may be inaccurate, but it's much better than nothing.
If BikeHike says 3000m for a 200 km route, I know it's going to be a lot hillier than a route for which BikeHike says 1500m.
Yes, that basically is the point, relative comparisonos between events, but no absoulte value you can rely upon.
I did the Cestyll Cymru 200, which had AAA points, but my Garmin (altimeter) recorded less than 1% elevation ,which is the bare minimum for AAA points. Once plotted into Strava that figure became even smaller, which is typical of older Garmin when coupled with Strava. In that particular case, I feel the AAA points were a bit of a free gift of topographic estimates.
Average speed doesn't lie either, if I average nearly 27 km/h, it can't be that hilly...
* plus or minus 50%... well, just choose a route of your liking, find it on Strava and look at the different elevation people have for exactly the same route... You will see wildly discording figures... if you were to work out a mean, the spread wouldn't be too far off a + or - 50%