Some thoughts here: I agree that mostly you can simply not use it - this being said, I would argue there are several ways it impacts as well on player who dislike the feature.
Firstly, it introduces more separation between the class a character has mechanically and which class fits from a story perspectives, and it limits the story in some way. Consider Khelgar being able to become a a monk in NWN 2 or some of the characters is SWKOTOR becoming Jedi down the road. Such a feature is awesome but would not really work in BG 3 since you can do those kinds of respec anyway at anytime. Generally, I believe separation of game mechanics and story is an issue with BG 3, another example being the Str and Wis scores of a certain famous ranger.
More examples would include the class strongholds of BG 2, which would also not deal well with respec. So it at least limits what the designers can do.
For example,
Shadowheart switching cleric domains could make sense at a certain point of the story. But you'd need to do it yourself via Withers.
Secondly, it becomes part of the metagame, which some people enjoy especially on their x-th playthrough. At some point people will ask for advice on no-reloads games and other high difficulty playthroughs and will get guides and video recommending respeccing several times. It's already quite commonly done for multiclass builds that take up to level 8 or more to become effective.
Admittedly, this one is of low concern to me personally. But I do like tight story/game mechanics integration and unlimited respec does not sit well with me in this regard.
