Why were you forced? html5 was around at the time (and in fact twiddla was launched two years before flockdraw).

Open the same Flockdraw URL in two side-by side windows and draw in one of them. Compare that to the WhiteboardFox video or Twiddla demo.

WhiteboardFox says a few seconds is "fast syncing". Flockdraw's sync is realtime (try it for yourself).

The kind of latency and overhead I wanted when building Flockdraw is only really feasible in JS when using WebSockets (which wasn't even fully standardized until 2011) but was doable in Flash in 2009.