I have half dozen Hue bulbs, and they seem rock-solid - far more stable than my Lightify bulbs.
The HA SkyConnect does seem to be a factor. For a while, my Lightify bulbs were the last thing on my old Samsung SmartThings hub (via the HA integration- basically using the ST hub as a Zigbee radio/stack), because they operated more reliably there.
Yes, every line-powered device is (probably) a repeater. Many light bulbs are, with the caveat that you must keep them powered all the time. Having a bunch of repeaters drop offline will cause fits with your mesh stability.