the game also originally intended for you to have one healer with strong shields but piss poor direct healing and one with basically no shielding options at all, that is the reason why ast originally was nothing but either a bad whitemage or a bad scholar, and what is still keeping them back as far as adding healers are concerned, "it was originally designed that way" is a non argument, monk was originally designed without any group buffs, Bard was originally designed being able to support others, fights 5 years ago being designed around having 1 of every of the original mustn't be an argument against change
i'm really not sure what the ranged role being inflated should have to do with that, gonna let the cast time argument stand as a reason for the distinction because arguing that wouldn't lead to a satisfoctry result i believe, but "we have to many "ranged/casters" compared to melee, lets split them up into seperate groups" solves exactly nothing ? having 2 groups of 3 competing for 1 spot each if anything is worse than having a big group of 6 competing for 2 spots as far as enabling different class compositions, which was squares goal time and time again when "the meta" got brought up.
which if the 4th slot would be free and classes were equal would sort itself out by itself, you would allways want 1 melee for a)the 1% buff and b)the melee lb, the by far most universally usefull dps lb. yes, you might not need that in every fight but you also might not need a physical ranged to kite some shitty mechanic in every fight. IF the 3 options would be equally viable, with no extra push from square to "take class x" , all classes were perfectly balanced, 2 ranged were a given (1 physical+1caster, you yourself said they were their own groups, which is actually exactly why i think they should be one group, than you could balance around 2/2 and would "only" need to keep the numbers of classes equal"ish") you would take 1 melee for the 1%+lb at least (remember, classes are really really well balanced in this scenario so no reason not to take a "free 1%buff+at least the option to single target lb") so why cant the 4th slot sort itself out ? you scared all these bards are gonna take away your ninja slot with their "free movement" which they won't use on any mechanic as there are allready 2 ranged doing them ?