Having both types within the game is what causes all the hullabaloo, because two of the three Broad classes are the two purely MARTIAL classes in the game. Which means it gives the impression that the game is focused on magic because there's all these other spellcasting Classes in the game and only "two" Martial classes. But that's not really "true" per se... because all of what WOULD be the heaping amount of Martial classes are actually presented as subclasses under two Martial umbrellas. The Samurai, Thief, Scout, Assassin, Swashbuckler, Cavalier, Gunslinger, Banneret, Champion, Mastermind et. al... could ALL have been their own Classes in the game sitting right alongside the Cleric, Wizard, Warlock, Druid et. al. And if WotC had done that, there wouldn't be any of this caterwauling about not having enough Martial Classes.
I think this is also where some of the wackiness and imbalance of subclasses comes from.
The Broad classes like Fighter have a ton in their umbrella so TSR and WOTC had a ton of directions to go with kits and subclasses at the expense of doing them all poorly.
The Semi-narrow classes were planned with only so many subclass ideas and once they go passed that number, the designers struggled for ideas and this is where you got broken and boring stuff like Twilight/Peace clerics and CODzilla.
And the focused narrow classes had planned splits so they had well made flavorful and balanced subclasses as long as you don't force an idea into the class without the design space (Beastmaster/Way of the 4E).
Narrow just seems objectively the best option but (current) WOTC and many fans just hate the idea of new classes.