Enemies not having access to weapons with the same ranges as the players is a system problem and most systems have some sort of readied action, so if the player is doing the in and out dance, they can ready an attack for that.
On top of that, there's usually a penalty for attacking from that far away. Unless they're able to move into and out of their optimal range without being attacked, which would again be a system problem.
They've isolated themselves again by staying so far away. If the rest of the party isn't in the fray, the enemies can run for cover. This could mean they escape, or pin them down. The latter meaning the flying player is using their abilities for teamwork.
If the rest of the team is in combat, then there's one fewer target. This can be good or bad. It means the tanks and healers have one less person to worry about. Or the the team gets focused down faster, fucking over everyone.
They're also open to ambush. No one else is near them. They're fucked if something gets a good hit on them.