User blog:Edrea/Is Morgana more powerful than Merlin?

I am wondering, Merlin is supposed to be the most powerful sorcerer ever walk on earth right (so it's said in the series), but in some cases it doesn't look like it. Here are some examples :

One, the most obvious one : Killed by mortal blade  Morgana said that she was the high priestess of Old Religion, she can't be killed by mortal blade. So, when Percival (or was it Gwaine?) stabbed her in the episode The Diamond of The Day, she didn't die or appeared wounded badly. But Merlin, in A Servant of Two Masters appeared wounded quite bad after a man on the horse clobbered him and then  in The Kindness of Strangers almost died after being wounded by an arrow. Even Dochraid has to be wounded by the Excalibur in The Hollow Queen. Why Merlin appeared so weak?

Second : The Ageing Spell  First when Merlin disguised himself into Dragoon the great in episode Queen of Hearts, Merlin used ageing spell. In the end, he needed potion to return to his former self. He couldn't make himself back by using spell again (was this because he was not powerful enough?), and then again in The Wicked Day, A Servant of Two Masters, and in With All My Heart. But Morgana, she didn't appear to be using any potion at all chaging into Hilda or back again. This is getting weirder, later on in episode A Lesson in Vengeance Merlin even had to drink the potion to turn INTO Dragoon, not just turning back FROM Dragoon.

Only in The Diamond of The Day that Merlin didn't appear to take potion back from Dragoon (although he might have to do it but it was not shown in the episode or he didn't have to take it anymore since he became the greatest sorcerer after emerging from the Crystal Cave).

Did I miss something here?