Yeah ! But i don't think it's the reason !
The allied clans became weaker beacause fighting and sealing a foe as strong as the demon clan took a toll on them ( especially the goddesses) and also because since Brittania has been peaceful ( for a long period of 3000 years), the clans got rustier and therefore grew weaker as time passed !
As for Escanor, if that theory is confirmed, then he most likely has an important portion of the magic power but i don't think it's as high as 80% ! ( even 60 % seems too high to me) Perhaps he has 50% ! He got half the power all for himself which is still pretty impressive considering how humongous that power might be !
Zeldris made it clear that this magic power was abundant in the LAND of Brittania and it was confirmed by Fraudrin saying that the earth itself contained that power ( which is now present in humans, animals and plants), so no, that power wasn't possessed by a single entity !
Would have made it much cooler if that were the case tbh... but, then again that does coincide with the fact that nobody has ever seen a human as strong as escanor and Sunshine as an ability is completely foreign to the commandments. Could be that the reason it no longer exists is because someone actually got their hands on it though! That'd be a pretty insane sin of Pride, for example, don't you think? If your first incarnation waged wars, killed people and basically hinted at clans to fight one another just so you could take the power for yourself? Basically, the ultimate form of selfishness by removing that magic you basically stick up the finger to all the clans who fought for it? And then you realize how much you lost in the process and deem it a curse and not a gift? Maybe that is why Escanor cannot control it? Because it is not a magic that should be controlled, because it doesn't belong to anyone? That would also slidify why it is a curse!
As for how much of the power he has inside of him... if he only has 50% of the power inside of him and reaches like 100K at noon (for example) that means he could reach 200K with 100% of the magical power. That is basically saying GG to every living thing if he gets his hands on it all, would also explain why everyone wanted it though
i wonder if Gawain will show up in this storyline at some point and maybe be an angel to fight Escanor, because he will have the rest of the power? Who knows... but, as for right now, it seems like it might be the case! Or the sunshine like thing could just be a representation of the goddess clan overseeing the fight?
