FormerlyHemlock
Hero
Tru dat, but we need to begin somewhere
A relatively simple partial fix is to allow enemies to drop prone using their reaction when fired at with ranged fire. Combine with high AC enemies for best effect.
Result: ranged fire makes enemies drop prone, making it harder to attack them at range and easier to attack them in melee. Ranged fire continues to pin the enemy in place while the melee elements advance to engage them at advantage. Combined arms can exploit the enemy's posture better than melee alone or ranged alone.
The other half would be to remove the absurdly-short range limits on monster powers. Instead of a Medusa paralyzing "anyone who sees her within 30'", just make it the old-school "anyone who sees her face". (With the obvious caveat that the DM will rule when she's too far away to be seen, so e.g. no petrifying beings on other planets just because they look at your planet. Obviously.) That removes one of the major rewards of staying at range.
One additional touch is to throw in some occasional highly-mobile enemies with ranged weapons of their own, such as griffins or mounted hobgoblins. The PCs will then voluntarily retreat onto terrain where close-quarters fighting is more appropriate, e.g. into the woods, where the slow dwarf can clothesline the hobgoblin and then bust his skull with her axe.