Sparky

Of the surviving members of Cas's garrison, we have: 1. Anna, who fell; 2. Uriel, who secretly worked with Lucifer, 3. Cas, who, you know, and 4. Balthazar, who jumped at the chance to toss his heavenly duties aside for sex and booze.

Contrast that with two angels that keep it together (Hester and Inias)?

That's a lot of rebellion for a group of angels, given that everyone tells us over and over they don't really rebel. So what gives? If there was that level of disobedience in the ranks of Heaven, it would have imploded long before the first episode.

So the theory is that the reason you have so many problem angels is that this garrison was where they put the misfit toys. The angels that didn't fit. Safely under the supervision of Zachariah.

And IF we adopt that assumption, it leads to the further conclusion that this garrison wasn't chosen to take Hell because they were such great fighters, they were chosen because they were expendable. They were canon fodder. It was a win-win for Heaven. Get rid of the problem angels or achieve the goal. The garrison thought it a great honor, while their superiors sent them in because they didn't care if they lived or died.

And the worst part is that Cas would have died with a smile on his face, believing he sacrificed his life to further the goals of Heaven.

And that's another thing. People talk about Cas reducing his worth to his utility. But it's not some low self-worth thing. It's not him undervaluing himself or misunderstanding what the Winchesters think of him. It's because that's what he has been told for millennia - that his purpose is to serve Heaven - and now that he has put his faith in the Winchesters, it's to serve them, even through sacrifice.

Ok, so here's the fun bit without textual support. What if the plan was to have the entire garrison die all along so Michael could stroll in, smite some demons, make a big deal and have the righteous man immediately be impressed with his power and grateful for being saved. Oh, he wasn't going to get his hands dirty, but once the way was clear, Michael could retrieve his sword with the confidence that he would be so grateful that he would immediately consent.

Dean/Cas Rule No. 28: Always make good use of dark corners.