I don’t see what’s wrong with me disregarding or breaking FR canon if that’s how I want to play the game. It has no impact on anybody else’s game and there is no mechanical advantage to it, so if you ignore this feature you miss out on nothing.
It's not about what you do. After all, you can mod the game to be unrecognizeable and nobody will care.
It's about Larian actively supporting choices that break the integrity of characters. This is not like DOS2, where classes are just loose collections of starting skills and say little about the characters you assign them, and where characters' stories did not require specific abilities in almost all cases.
I think it's more like Larian supporting gameplay, and knows that an option like this can improve replayability.
Can you elaborate on how it improves replayability in your view? If I can try any class and any party composition at any time I want in a single playthrough, that's one less reason to replay the game.
I don't really get the "try any class and any party composition in a single playthrough" thing. If you respec a character at level 10, you haven't played that character from level 1 to 10, you haven't played that party composition and classes during the playthrough. I mean, unless you save and reset before every fight and every section respeccing everyone to try every possible different permutationts, but doing so your run would last easily 10.000 hours.
The way I would use this is playing the game once, maybe twice, as it is, THEN making weird runs where I change companions into something else. I would change them from the get go and bring them all the way through, with those classes facing the whole game in a different way. I would be able to do the same thing with faceless hirelings, obviously, but I find that hirelings are kinda boring so I rather respec the companions.
