But you are not guaranteed to be able to stay ranged, even with high mobility.
The idea that the players can *choose* some kind of "all-situation optimal tactic" is not supported by anything. Context defines what tactics ends up viable, and trying to argue that melee is """inefficient""" without any context is just the old "perfectly spherical cow in a frictionless vacuum" standard.
Indeed.
Yeah, that's another factor to consider: NPCs can easily be more numerous than the PCs, and if they are then *they* are the ones who will be advantaged if you try a "ranged showdown without the ineffective melee stuff" and the DM doesn't consciously choose to spare the PCs.
You want someone capable of threatening the NPCs in melee, so that they can't just select one person at range and go full ham on them.