I've re-read Paul's initial post three times now and I'm still not seeing how you're interpreting the message of his post as "DAWs aren't mean to be used by musicians".
All he's said is that introductory products in the domain like Garageband (or perhaps Ableton's new app) initially start out as stepping stones for musicians who don't have an interest in the engineering aspect of things and that as the musician gets drawn into the discipline of audio engineering those apps become insufficient for their needs and they end up being drawn into full-featured DAWs.
He was simply highlighting an interesting problem that many musicians encounter as they dip their toes into the water of recording their music for the first time.
That aside, he very clearly refuted your three assertions:
1. That ALL engineers are musicians: His examples are correct (Though I believe CLA may be a drummer, if not a great one.) There are still plenty of other examples to draw on.
2. ALL musicians have a grasp of music production: His example of classical musicians is spot on.
3. EVERY DAW is developed by programmers who are musicians: I can't speak on this, but since he's a DAW developer, he'd sure as hell know a thing or two about that.
I don't know where you're getting this "holier-than-thou" attitude from. He's just having a conversation. There would be far less cause to refute your points if you didn't speak in so many absolutes ("All", "every").
Take a deep breath, man.