I don’t really understand the context of these messages.

The one about MCAS running rampant is clear enough but what does he mean saying that he sucks at flying? What is egregious?

I interpreted that as “I may be a bad pilot but MCAS made my trying to fly in the simulators particularly unsuccessful”

Nope he was complaining they made changes to the MCAS without telling him and he was concerned the simulator wasn’t accurate to the planes actual experience.

Those are the pilots words and he’s saying the messages are being misinterpreted and cherry picked without context.

That's not what it appears from context.

He was joking, as if you'd be a professional F1 pilot and when testing a new car you would say "I suck at driving but this thing loses grip in the corners".

I read it as self-deprecation. Something people do to take the edge off of bad news.

Think about it from a Dunning-Kruger perspective. The more you know about flying, the worse you think you are. The pilot is an expert and very experienced. He knows what he doesn't know.

He's acknowledging that even with all his experience, he could be wrong -- but clearly he wasn't.