Yeah.. riding based on outdoor GPX/FIT/TCX files are fully reliant on the accuracy and dependability of the barometer (and perhaps weather) to get good and proper / nice gradient profiles.
BreakAway does try to smoothen out the altitude data a little, but it’s not as great as it should be. I’ve tried gpxmagic, some other smoother but all of it depends on the quality of the input data. so… YMMV
w/ regards to zwift, here’s a GPX profile of the 3Sisters Route ( I took this route from strava). There are spikes, but possibly lesser.
