Depends on the stage volume. If it's moderate and the wedges aren't loud, then they augment the player's mix in a natural, musical manner. But if they are used to overcome loud stage volume, and are therefore even louder themselves, then you encounter hearing damage and ear fatigue, and in the case of a drummer, play differently to match the monitor volume.
it also depends on the specifics of the mix. That is, if you're using a click or tracks, you wouldn't use a wedge.
There's another aspect of a good mix - is there anything you don't want to hear? If so, in-ears or phones are a better alternative to a speaker.
In any situation that requires monitoring, if I'm given a choice, I take the in-ears every time. I find that in-ears fed through a personal mixer give me great control over the volume and I have learned to set that volume at levels that encourage playing at appropriate sound levels. It also puts the sound inside my hearing protection, as opposed to having to listen through the hearing protection.
I won't say I've never had a satisfactory wedge mix, but I can certainly count the occasions on available fingers, whereas I have gotten very accustomed to playing with my in-ears and getting a workable mix with little effort most times.
I dont like in-ears, I have always felt isolated from the rest of the band and the audience. The sound isolation is great, and everything comes through loud and clear, but between the setup time and the isolation I would rather have wedges.