Minsc is iconically a ranger/berserker (certainly a martial class) - *defender* of the witch Dynaheir. His introduction in BG1 explains this setup and that is how most people encountered him. Sure, you can add some other class to his initial choice later, via multi/dual class, but to remove the original martial/ranger part from his 'kit' (and make him a wizard) is to rewrite his backstory and pretty much disregard FR canon.
Some may be fine with that - others who have an attachment to BG quite likely won't. I'm certainly not.
As for the origin characters, they have stories which seem clearly linked to their class - some, like Gale, more tightly than others - and simply deleting that class identity will, in my view at least, weaken the coherence of their stories. Laezel as a bard for examppe? :o No...
If people don't want to play an origin character - create a bespoke character/party. Larian have provided for that.
