Fill elevation and filter
When I generate a route with BRouter I am yet to see a total ascent estimate that is less than the actual recorded track. This is hardly surprising given the SRTM height data and method of calculation. The route chart often contains a lot of artificial noise. The calculation is generally worst where the terrain is more hilly. Just the situation where it may matter the most in deciding a choice of route.
There is already a track function to "fill elevation" however this can be performed multiple times and won't change subsequent values. My suggestion is that a 2nd pass of the function or new menu "Fill and filter" would apply an appropriate low pass filter to the track to remove high frequency components.