I feel he has made a case for some inadequacies in Xz. Some of the claims seem exaggerated, such as (2.2) the optional integrity checking, assuming the decompressor at least logs the fact that it couldn't do the integrity checking. Some others are clearly more significant issues, such as (2.5) not checksumming the length fields (2.6) the variable length integers being able to cause framing errors. Others still are petty, such as (2.3) too many possible filters.

While I think he made a case, I somewhat doubt that the other formats are flawless, and the real answer would lie in a more open analysis of all of them.