Hmm. Going up the chain doesn't mean that the topmost layer will be any more solidaric towards those remaining behind.
Although the Black Plague probably was a period with accelerated influx in the nobility, it doesn't follow that those comprising the nobility lost much power over their remaining (or new) subordinates.
Personally, I'd favor the middle of the 17th century as the tipping point, where effective royal absolutism at the expense of noble power
by means of civilian bureaucracy had its heyday.
The bureaucrat was in no position to build up a gang of followers or a landbase to start a feudal fragmentation of power, as had been the perennial head-ache for kings for centuries.
(The Norman monarchs of Britain had sought to prevent such fragmentation by splitting up the lands each noble had, the Germans uder the Ottonians had tried to make celibate bishops into competing potentates (and with less ability to feudalize for the benefit of their..progeny).)
But once the nobility's power had been curbed by the absolute monarch (with bloody rebellions like the Fronde), the civilian bureaucratic society had no use for the monarch either. His head might as well be lopped off...