So imagine a chaotic evil character, Mr Moneybags, who selfishly wants to become wealthy and is willing to break the law and kill other people to acquire wealth. However, what if Mr Moneybags learns that it's more efficient to acquire that wealth by being friendly and cooperative and by following the law? Then why not do that instead?
What if a law abiding character learned it is more efficient to kill and steal to acquire the wealth? There should also be nothing wrong with doing this.
Being "chaotic evil" alignment doesn't mean becoming
the murder hobo. Sometimes being evil means being good. You catch more flies with honey and all that.
Sometimes being good means doing evil.
Honestly, I think the whole alignment system in D&D is just a bit of lazy convenience anyway that really just ends up getting confusing once you start telling complex stories. Alignment isn't a big thing in BG3, and seems to be getting phased out of D&D in general. I approve of this.
Agreed. It seems to make people feel they "have" to be a certain way to fit into their alignment rather than doing things naturally.
If a character is "stupid evil", then they are by definition flawed. Like Mr Moneybags for example -- a character who's too stupid to realise that murder is not the only way to get rich. If Minthara is doing something stupid then that's a huge opportunity for a character arc.
Being evil does not mean being stupid but it does show up in all alignments. Mr. Moneybags might actually be very smart and decided murder is the most efficient way to getting rich.
A character arc doesn't always mean "become nicer". Sometimes it can be the opposite. Many stories have been told where the climax is the protagonist learning to "love themself more" or "fight back against the bully" or whatever.
Your examples here aren't really the opposite of becoming nicer.

Good is definitely not nice a lot of the time anyway.
Character growth and development is always a good thing but the constant general assumption that evil always needs redeeming is just tiring and annoying. The rare times a good character turns evil usually get screwed up too, they always have to regret it and get sucked into the redemption crap as well. I hope for more options rather than the same worn out and unrealistic stuff that shows up everywhere.
Don't really want a redemption arc as such. More so somewhat wholesome development. Something along the lines "I can trust MC" while still being somewhat evil. Preferably not baby kicking, mustache twirling variety.
I just hope Mithara doesn't devolve into: "HAHA, i really don't care about you, here have a backstab!" at the "first" opportunity.
Any sort of non redemption development option would be fine with me. It really should be hard to gain her trust though, and depending on choices made there may be some backstabbing along the way.