For me the performance seems better. It also seems strange that if one of their two main publicly stated goals was to increase performance (the other goal being ease of maintenance), that it would slow down. Maybe you have extensions interfering?

Also, the set and scale of features in the Facebook app makes it literally one of the most complex webapps out there. It's far more than just multimedia posts+messaging -- it's a marketplace, dating, games, apps, groups, pages, and more. Nobody's "failing". And the 2MB of CSS was the "before" uncompressed. The "before" compressed was 400 KB, and this update appears to reduce it to under 80KB compressed. That's 96% less than the 2MB you're complaining about, more than an entire order of magnitude.

So Facebook seems to be improving here, no? I fail to see what is a "total failure" or "clearly a problem".