He seems to phrase it as though he has to, that he falls back because nothing else works. What would you suggest instead?

I'm only lightly familiar with both Cocoa and SwiftUI, but I have heard many nightmare stories about SwiftUI and Swift the language. I'm inclined to take his criticism seriously, and I think there's a big distinction between people who know a platform very deeply -- you are a strong expert almost everywhere you touch :) and it's clear from your comment SwiftUI works for you -- and normal developers who, you know, just want to learn a framework once and use it to get a job done. Living in the past is not necessarily bad; it's a good thing if what worked in the past worked well and still works today.