Rangers can not make the same dmg as meele, simply because of the concept of beeing ranged.
There wouldnt be any reason to choice meele (except for taste), would ranger have the same dmg as meele. Without the risk of beeing meele (in most cases is it more risky to be close to the enemy, some even have traps for meele, by casting very fast close aoe attacks, without warning).

Best example, but off topic, is the sneak archer from skyrim. He make the biggest dmg and has the advangte of range. There is practicly no reason, to not play him.
Something similary would be, if the rangers in this game had the same dmg.

Caster have the distance advangte over the meele. So, they make less dmg. But, they are above the Rangers, because, they attack slower, can at some points not attack. And, have in theorie a limit of there attacks (mp). In theorie, because, Blm has practicly endless mp, because of his ice phase. And at last by a puppet was i not able, to reduce my mp to zero, when i tested the summoner.
But, the concept is there, that they have drawbacks, that justify there advangte over rangers.

What drawback should the rangers have, when not lesser dmg than the other two?
Limited attacks, like ammunition, that would be similary to mp?
Lesser hp/def for beeing able to run away from enemies and attacking at the same time (was in the story sometimes usefull).

Or other question.
How much is the difference of rangers vs meele, if the meele is not able to use allways position?
True North is limited and bosses are moving so much around or are so big, that it can become hard, to allways use the Extra dmg of position (i dont bother much with position, when i play meele, because it is a pain to try to hit each time the right side).

That the mch is making lesser rdps is simpl coming from the point, that he act solo. Where the other two obtaining there rdps by taking some numbers from the partymembers, who obtained bufs from the ranger.
It is practicly 8 vs 1 in this case.
Are most partner are weakened or dead, is the number of this two lower and the mch has the upper hand.