It became the norm that using stickies in DM/MGE is frowned upon for a long time now. Same with using shotgun as soldier. I never agreed with it, because yeah, it can be important to practice your pill / air rockets, but that doesn't mean that stickies and shotguns aren't important / don't require practice.
All weapons have very practical purposes in a lot of situations. Just because one person is going for air rockets while the other guy is using a shotgun for anti-air doesn't mean you have the right to demand it to be played your way. Unless you want to play against a Demoman in DM / MGE in a very impractical scenario where he is using pills 100% of the time, then I would imagine that you would want to put yourself in the position where you need to beat him as if it was a scrim / match (ie: he is using stickies and pills).
Stickies can be frustrating to play against, but I think lower-level players just think the "stickies are op so you're not really good" card is an easy card to play. If you would like to think about it this way: a better player would beat you, even if you are using stickies.