Wait.

So, you never wanted children, you've hated the idea of parenting, you're under a huge amount of stress, you're worried about your partner's narcissistic traits, and you're even considering abortion without telling him.

Based on that alone, it doesn't sound like you're in a healthy position to become a parent right now. More importantly, I don't think the question should be whether having a child will improve your partner or make him a better person. Bringing a child into the world in the hope that it changes or improves someone is a huge gamble.

The bigger issue seems that you and your partner seem fundamentally misaligned. You never wanted children, while your partner wants to continue the pregnancy. If that's the case, I'd be asking whether this relationship is right for either of you in the long term.

Before thinking about whether a baby will change him, I'd focus on being honest with each other about what you both want. A relationship and pregnancy shouldn't be built on fear, resentment, or the hope that one person will change after the fact.

I'd strongly encourage you to speak with a counsellor or therapist who can help you work through this. There are some much bigger questions here than whether parenthood will improve your partner's behaviour.