David Marcus vs. Jack Crusher

[McAvoy]

The death of his son was still important years later when Praxis blewup. But he was more upset losing the Enterprise than David?

You're right, that's a legit mad take to think that.

I'm not sure Marcus and Crusher are all that comparable. Marcus exists purely to service Kirk's character arc and in that he does great, but he's never really a character in his own right. We care when Marcus dies because of what it does to Kirk not because Marcus is in anyway compelling in his own right.

Crusher though has a lot more work done to make him a character in his own right. He's not just there to put Picard through the wringer and give him an arc to go through. He forms his own relationships and it's fun to watch him do so. That he works as well as he does even with the overplayed Borg reveal is rather impressive, and it's credit to the actor and writing for him. Even more so as I initially was not at all sold on the guy, and thought he was probably going to be insufferable.

This is what Marcus is and that is all he is and that is all is needed. Two movies and a cameo/motivation for Kirk in ST6. Crusher is different because he is written as his own person, character. Benefit of even having ten episodes of screen time in a overarching season long story that actually involves him.

Marcus despite two movies doesn't have that at all. None of the movies were about him and outside being the guy responsible for Genesis falling apart, he isn't really directly contributing to the story on his own.