Tough to know where to start. Pretty much every fact asserted in this piece is without any real evidence.

Starting at the end >This change occurred as a result of William the Conqueror’s defeat of Harold Godwinsson at the Battle of Hastings in 1066. As a result of this, William claimed that he had won the whole country by right of conquest. Every inch of land was to be his, and he would dispose of it as he thought fit.

>All land was thereafter owned by the crown. Perhaps in this can be found the seeds of the desire by the lords for the Magna Carta

This is simply not true that William claiming this was somehow new or novel. Lots of kings did this at the time. The Anglo-Saxons by Marc Morris illustrates this well.

Further, yes the dark ages were decentralized, but not at all because of the reasons in the piece. They were decentralized because the was an era of incredibly high friction. It took forever to get anywhere, to tell anything to anyone, to trade, to make deals, collaborate, to organize people. A bad harvest could wipe out a decade of hard labour building up a community. In that context there were just very few centriphical forces pulling things to the center.