"'the benefits of cross-platform development weren't enough to outweigh the downsides of HTML5, which pulls in data much more slowly than native code,"
Pulls in data much more slowly?
Is he talking overhead of HTTP headers? Handshaking on websockets?
The worst part of the facebook app has been the fact that when you load it up it wipes out the screen of any data you had last time, then pulls in a full new set over a crappy mobile network connection which very often timed out. Had the app cached (HTML5 localStorage?) postings and displayed what you already had, while trying to get new ones, it would have been much more useful.
He can blame HTML5 all he wants, but poor design decisions could be made for any language and platform.