Just updated to 2.5.5 release, and to my delight I discovered some new items in my Paper UI Inbox:
HUE native groups 
Using these groups enables group-unison actions without any visible delays.
More here: https://www.openhab.org/addons/bindings/hue/
Only thing missing now is: https://github.com/openhab/openhab-addons/issues/7742
and I can do away with all my http PUT via REST.