I don't understand how your first two sentences are contrasting assertions. Combat role is a part of the character one wants to play - eg do I want to play a skirmisher, an archer, someone who wade into the thick of melee heavily armed and armoured?I never choose a character based on combat role. I choose based on the type of character I want to play.
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I never, ever think about the combat role I play when picking a character. The concept of defender, controller, leader, or striker is so foreign to how I go about choosing what to play.
Maybe that's not something you think about. Speaking for myself, 4e D&D was not the first time - in the context of party-based, combat-heavy FRPGing - that I thought about PCs as archers, heavy melee, skirmishers, healers etc. It did systematise that thinking.
Yes. 5e D&D is not the same as 4e D&D. 4e D&D also permits a viable, non-magic-using, DEX-based skirmisher and archer. You just need to use the ranger rules rather than the fighter rules to build that character.A DEX-based fighter is easily viable in 5e. They can be a much better archer than a ranger.
In 4e D&D, a high CHA, low STR and DEX paladin is quite viable (I know, I GMed a game from 1st to 30th including that sort of character). I don't think that would be a very good build for a paladin in AD&D or in 5e D&D.
And I can easily play a healing INT-based magic-user in some FRPGs. But not so much in D&D, which tends to make healing the province of clerical types and, more recently, bards. An exception, of cousre, is 4e D&D which permits completely viable low-INT and low-WIS healers (namely, Warlords).
I don't see what is meant to follow from any of this, other than pointing out that different sets of class-based rules have different ways of using their classes to carve up the terrain.