Second, overall attendance at unofficial events was significantly lower from previous years. Previously you faced huge lines for most parties, but many such lines, if any, cleared quickly this year.
Third, investment by startups in their own official events was significantly lower this year. Startups either attended without running their own events or participated in other party's events instead of running their own events.
Fourth, many large brands decided not to participate this year. Microsoft and Samsung were both absent for the first time in a long time. And many other companies scaled back their events.
Fifth, as you mentioned, the exhibition hall was dominated by non-startup parties moreso than in years past. This indicates that startups are not investing in SXSW as much as they had before.
In general, attendance felt lighter this year vs. 2016, and definitely vs. 2015 and 2014, which felt like a peak year for SXSWi.
While these are SXSW-specific numbers, I would wager that you are seeing similar slowdown with other startup-focused events and conferences. Meetups are more lightly attended, and certainly less sponsored.
It feels like the burst in activity is slowing. Not gone. Just slowing.