Take or leave what I have to say, but I am sincerely trying to help.
I have read your posts and find some of what you say to be very frustrating from an AC perspective. I am writing this sincerely because I didn't want my relationship with my mom to end, but I chose to do it anyway. Some here find that to be a cruel decision but I really am only trying to give myself space to heal and feel safe. If someone had talked to my mom maybe she would have made different decisions. I don't want those regrets for you and your son.
I really don't think any of what you've said will help the situation. First, I think you should work on how you think about his partner. I know you're convinced she is controlling him. Maybe she is. But to them, you won't come out looking like a concerned mother to them. If you've miscalculated and he is very happy in his relationship, this will lead to your estrangement. They are having a child, and I hope you can objectively see that they want to protect their child. I'm positive you wouldn't harm the child but as new parents you need to understand that if you don't feel safe to both of them, they won't want to bring the baby around. You must feel safe to his spouse as well.
If she is problematic, that will come out in time. Your son will not feel safe to come to you for support if something happens there and he knows you don't like her. Adult children can be very sensitive about their parents acceptance of their life choices, and choice of partner is a big one. If he has to choose between you and his wife and child, I don't like your odds. So don't make him choose.
As for saying he hasn't experienced real hardship or trauma, please please dont say that. He won't agree and it will not mend the relationship. Regardless of the truth of the matter, this is not an argument that builds bridges. My mother has said this to me. It was inaccurate, but also massively hurtful.
Finally, I will say that as an estranged adult child, I have heard "life is too short" and it doesn't have the effect you think it might. I agree, but I feel that life is too short to go around in circles with someone who doesn't listen to your perspective or see your own struggles. This will not be new to them, and will sound like a dismissive platitude. It might help how you perceived the situation but you can't force that realization onto someone. Keep it for yourself and your own healing. Your son would come away from these discussions feeling misunderstood and belittled which I can see is not what you want. That will happen. I promise you.
My best advice is to press pause. Deal with yourself and your own grief (as you are) and be polite to your son, ask after his partner's health (and only her health), and then stick to safe topics. If you do this and don't try to convince him of anything, I do think he will come around after they've settled in with the child. Madgrans advice from earlier was spot on with how to handle those conversations that go bad. Polite distance and nothing that could be perceived as manipulation.
I understand the rejection is painful. It will get better with time. But please don't feel like you can talk him into your side because it won't work. I don't say it to be mean or judgemental. I really think if you back away from a stance that anyone is right/wrong/at fault/controlling in this situation and instead think "I want to mend this relationship" that will help. The relationship may not shake out to look like exactly what you wanted, but if your son sees the relationship dynamic can change he will come around.
That's all I'm going to say. All the advice is meant sincerely and it's what I would have wanted someone to tell my mother. Unfortunately, she wouldn't have changed. But you're not her so I thought I would give it one more go.
Anyone with some snarky clap back ready can keep it to themselves because i won't read it. I'm posting in this thread only to offer help and now I'm gone.