Given that we're talking about cycling, the solution is to buy a power meter and measure rather than estimate. Unfortunately that's a rather expensive option for all but the most committed cyclists.

Being someone who has a power meter, I can say that strava's estimates over a long time period aren't that terrible, but if you're riding in a group, or there was a some wind, or a million other reasons they can be absolutely miles out.

That's hardly strava's fault, it's more about what's actually possible with an estimate.

What is completely made up and should be ignored is the calorie burn estimates you get from gym equipment.