Okay, excess resin in the seattube sucks, he's right on that.
The other issue, with the brake mount, he even says, he sprayed clearcoat on the frame and then wonder the brake mount is still uneven... Well that's not exactly clever but yeah understand he needed something more to complain.
Regarding the flex, look at how much the tire gives in, add a little bit of play in the headset area. All of this on a little elevated step and yeah propably not the most stiff handlebar ever also the C-shape ring doesn't really help tbf and you get such results... I'd say flex seems staged to me and would be solved pretty easy with another compression ring. Only real issue I see is the excess resin in the seattube