When you get down to it Asgard and the nine worlds is very similar to the world of D & D or other fantasy role playing. Yeah, the gods are stronger than "mortals" and long-lived, but that is about the only major difference and just about everything else in the nine worlds is close enough in power to be a threat to them.
With that in mind what defense do Asgardians really have against being transformed by a powerful sorcerer or god from another pantheon who knows how to use their energy-powers like Hera? Amora one time with a wave of her hand transformed Heimdall into a tree. The only reason he was saved is due to his magic sword. Thor is fairly immune because he is powerful enough even a sorcerer as powerful as Loki cannot really effect him. But what about lesser gods like the Warriors Three? In theory what is to keep Loki, Amora, or someone else from turning them into a rat? In the past such warriors have enough trouble with illusions and lower powered wizards. The only times an Asgardian seems to do well against a powerful magic user is either they have a long-distance magic weapon of their own, the magic user does not want to fight them (as in Karnilla and Baldur), or they just happen to be one of the lucky few who is so powerful magic does not really effect them. Maybe I haven't read enough regular tales, but this is the way it always comes across to me.
They don't have any defense, which goes a long way to explain the politics of the nine worlds. To survive warriors must ally themselves with a strong sorcerer and submit to their rule (Odin, Karnilla, Utgard-Loki, Malekith, etc)