You know, I wasn’t all that bothered by that. Luke was always a bit impetuous, and who better knows the damage a resurgent Dark Side would cause? Luke isn’t a Jedi because he nearly kills Vader – he only becomes one when he throws away his lightsaber.
One central truth becomes more clear the older I get: people grow and change but the core essence of their being remains the same. For all his Jedi wisdom and experience, Luke will always have a streak of impulsiveness that is self-destructive. It’s just who he is. The Jedi Master we find on Ahch-To is depressed and withdrawn, but it’s the same Luke we knew before.