since dashing into melee is possible in a single turn?
It is, but its not possible to dash and attack at once, since it both costs Action. That would still mean one safe turn ...
Action surge, cunning action dash, double cunning action dash potentially, and eventually we'll probably have multiclass fighter-rogues with cunning dashes and action surges. Dash and attack is very possible. Or dash and push, as it happens.
Also, it doesn't really matter if the dash is followed by an attack or not, because simply having some darn melee thing standing right next to your ranged character forces you to respond to that, which means the ranged character isn't using its optimal action on the optimal target.
Fundamentally, having maybe a single turn to shoot an enemy, particularly if we take away the high ground advantage, is just not enough to justify how squishy ranged characters are in melee. Do consider that 5E PHB contains the Eldricht Spear invocation for warlocks that gives Eldricth Blast a 300 foot range (~90 meters) rather than standard 120 foot range (~36 meters). Longbows have a normal range of 150 feet and a long range (attack with disadvantage) of 600 feet. Heavy crossbows are 100 / 400.
