The evidence has always pointed to Wuhan being ground zero, so calling it those names doesn't indicate he knows something we don't. And to your 2nd point, it is true that the WHO is at least somewhat in the pocket of the CCP.

It is true, it's not certain that intel agencies would know what's going on inside the lab. But I think it's probable that they would. Intel agencies are very well aware of the threat of biological warfare, and there are a number of efforts to actively monitor developments, especially in a rising power like China.

With regards to "political distrust leading to a lack of coordination", that is very much a pre-9/11 thing. I'm speaking as a former military member that had an SCI clearance and plenty of first-hand experience with what goes on inside the system. When we were getting briefed into the various programs, the lessons learned from 9/11 were widely cited to explain why the intelligence sharing programs are set up the way they are. There is a lot of cooperation between agencies nowadays.

With regards to the letter, it looks to me like a political puff piece.

How could he dismiss with such certainty that a lab leak was a "conspiracy theory"?

I think at that point, they probably couldn't. But you can find plenty of pro-CCP propaganda like this on the internet. At any rate, my belief that it probably wasn't manmade is based on what the people that I think aren't comprimised by CCP interests are telling me, not by what people like this are telling me.