"Full delegation of power over a territory"? Being a Duke of Devonshire has never conferred automatically any power, let alone "full power" on a hereditary holder.
Your confusing nobility, titles and feudalism.
Critically for a title appearing in 1694, one could think it have little to do with medieval feudalism, would it be only for chronology's sake.
Nobility, in its larger meaning, predated and existed after feudalism, and all nobles didn't had titles.
In its classical and general definitions (while pointing out once more that we're talking of a proteiform concept), feudalism covers :
1) Institutions and uses creating and managing bilateral obligations between a suzerain and a vassal, one of the obligations of the suzrain being to support his vassal by giving him a good, the fief. On the other hand, the vassal was to give support by military means as well advice duty: that's the feodal regime or better, feodalo-vassalic relationships.
2) In the largest sense, society based on this relations, and more generally, carcaterised by the hierarchisation of people and lands, domination of a warring aristocracy, shattering of public authority and of property rights : that's the feudal society.
And regarding something as
I'd precise that is less "my" standard, than a definition that's making the more consensus.
You can disagree with of course, but then we're not talking about the same thing.
Let's take a look at the english situation, in Middle Ages and not after (again for coherence purposes).
What appeared after the Norman Conquest was a quite rigid and idealized feudal system, sort of paramount of continental usages but for a quite reduced nobility (representing less than 1% of the total population, compared to the 4, 6 or even 10% elsewhere).
It certainly had a mark giving the specificities of english feudalism, critically a less important feudal territorial fragmentation, which made what's called in english "tenant" less important, and therefore the delegation of power (as in delegate : commit or entrust to another something)
Nevertheless, a much comparable system than continental one existed in medieval England. The
Armenian Genocide page about is surprisingly correct, so I'll advise you instead of copy/paste docs.
So, was England ever a feudal country? And if yes, precisely what changes made it into something else?
The same way Antiquity didn't stopped the precise day of 4th Setember 476, but was a longer process.
It's generally assumed that The Abolition of Tenues Act of 1660 represent a key date in this process.