@MrZoat  
In my own personal fanon I would like to imagine that magic is so rampant and wild within the land of Equestria that virtually everyone and every thing in the planet is very much infused with magic, it’s just that only certain kinds of life have adapted the ability to control or use this element of their own nature. You can exist in a world with light, but without eyes, you cannot capture it and thus cannot see in the way others can.
 
So in other words yes I think they’re magical creatures by default because they all live in a magical world, but no, they cannot actually do anything with this power - they can’t manipulate it. So with that, I’m not quite sure what this comic is trying to imply. I mean if we’re going to discuss classes of magic and say that unicorns are more mage-like, I’ve never seen any earth ponies that have druid powers.
 
I think it’s canon that changelings and Discord can drain earth ponies though, so this be further indication that it is actually there and can be corrupted/extracted. The idea of the cutie mark also seems vaguely magical.

Do Earth Ponies even have magic?