I think it's pretty clever.
There are a lot of usability issues with firewalls and proxies that make implementing other streaming protocols very difficult, and the HLS design basically causes the implementer to adopt a pattern that is resilient to those problems.
Networks got a lot better after Covid had everyone work from home so IT had to sort the hot-path out for videoconferencing. Nowadays I think WebRTC would be fine, but in 2009 I think HLS was pretty smart.