It feels like the line between Fighter and Rogue has gotten more and more blurred with each newer edition of the game.
There's a fine line between ALL the classes in the game. And that line is purely story and fluff based.
When it comes to game mechanics you can merge any and all classes you want. Clerics, bards, druids, sorcerers and wizards all have the exact same spellcasting slots and progression-- why do we need them separate? Fighters, barbarians, rogues, monks, paladins, and rangers all fight the same way, all use the same types of weapons, and all have the same small mechanical bonuses to damage. The only differences being one of those damage bonuses is called 'Barbarian Rage', while another is fluffed as 'Sneak Attack', another is 'Superiority Dice', or 'Divine smite', or 'Flurry of Blows', or 'Hunter's Mark'. But they all do the same exact thing... add extra damage to an attack.
The only reason and way we keep these classes separate is by arbitrarily designing story reasons why this is true. One of these casters "gets their magic from the gods!" while the other "studies reeeeeeaaalllly hard and figures this magic stuff out!". One of these warriors has "learned intricate weapon maneuvers that can knock an enemy down" while another one "cast a spell that knocks an enemy down". It's all just arbitrary fluff that has been used to make these mechanics SEEM different.
But it's not different. None of it is. Which is why 4E is what it is, because it made the evidence for this fact more crystal clear than any edition before and after. All the mechanics are the same regardless of the classes that use them. And it's only the stories that we attach to them that mask our eyes to this fact and try to convince us that these things are actually different when in fact they aren't.
This is part of the reason why the whole 5E Warlord argument has always rang hollow for me actually... as you can run the mechanics of a Bard as-is and have it work out pretty much as a Warlord. We just have to remove the illusion in front of our eyes that says "Bard mechanics are magical!" which was just completely arbitrarily decided upon by the writers of the game and which we all bought into.