> I think Habeas Corpus is one of the few clauses of Magna Carta that still has legal effect
I am not sure if it has effect because of the Magna Carta, but right to a fair trial is another right that still exists and applied to any "free man".
> I think it wasn't until Henry II that there were royal courts set up, to deliver the same law everywhere.
Yes, but that was still medieval. Yes, it was not one huge improvement. The Magna Carta was a step in a process that started centuries earlier and went to for centuries afterwards.
I am not sure if it has effect because of the Magna Carta, but right to a fair trial is another right that still exists and applied to any "free man".
> I think it wasn't until Henry II that there were royal courts set up, to deliver the same law everywhere.
Yes, but that was still medieval. Yes, it was not one huge improvement. The Magna Carta was a step in a process that started centuries earlier and went to for centuries afterwards.