I would only say that I didn't think Goodfellas or Casino glorified violence at all. Only in the Irishman it's a little more blunt. Like there's nothing at all dramatic about how Hoffa dies. Nothing sentimental. I thought at first that it would be like the Assassination of Jessie James, where everything builds up to a tense dramatic climax, but nope. It's pop pop drop end scene.
But yeah I read it as a look at mortality, at how surviving into old age can be more damning than dying young by violence.
I wish all that made me like the movie more. You could be right, it might end up being considered one of his best. For me, I can't see it outside of the context of his other mafia movies, and it just played out like a lesser version. I enjoyed it, but it didn't leave a lasting impression like his movies usually do.