I'm willing to bet that if you were to place the 4.7uf cap on the primary mains side of the cheap LED power supply instead of the 33uf, it would still virtually eliminate the flicker and the power factor wouldn't have gone as low as it did with the 33uf.
Was thinking the same thing. 33uF is too much, 0.3 is obviously too low, so why not try a mid point? It's largely academic since I wouldn't install hand-modified drivers in my ceiling, but this is an educational channel, soooo...
Anyway, the fluorescent lighting those panels are meant to replace can be as low as 0.6 (inductive), so it would still be an improvement if you can "only" get the PF up to 0.8 (cap) or so with minimal flicker. If there's still some fluorescent lights on the circuit then it could even cancel out to near 1 at the meter (not that's it's metered).