Hello
I agree with Antonio. The elevation data is highly over estimated. I'm not trying to compare with Strava or my Garmin GPS, but with official maps.
I rode several ascent where you have only uphills (no flat part or downhill part), and the altitude of the start and end points are clearly marked on official maps -> elevation is easy to compute. Every time the ploaroute elevation was too high. (some of the climbs were climbed by Tour de France, and measured very precisely)
Plotaroute remains a great tool I use all the time :-)
Greetings from France