@Militsiya  
I don’t think this means to say that these are characters necessarily motivated entirely by these vices, merely that they represent them in the way they act. Sure, Parasprites gotta eat like everybody, but the way they do, eating everything in sight and becoming a major problem, is meant to illistrate to the viewer the consequences of being glutonous, or of giving in to gluttony. Same with the rest

@Militsiya  
You are now one of my heroes. THIS is why I’m so drawn to antiheroes: counter-values and reversed perspectives turn everything into thought-provoking questions, and really make us think about who (if anyone) is “right” in a scenario.

Then how come that almost ALL of them had a relatively valid reason to back up their respective sin?
 
Nightmare Moon was created because Luna on her own wasn’t strong enough to take on her own sister, and teach ponykind a lesson about gratefulness, which, from her perspective, they deserved.
 
Parasprites have to eat to survive - like any other living being in existence! They’re parasitic by nature which they obviously can’t change.
 
Discord doesn’t follows any logic, and it wasn’t pride that caused his downfall - it was arrogance. He wasn’t proud of what he had done, he considered it natural, but irked ponies about it to gain attention.
 
Spike is the only one who’s “sin” is real - but then again, it is, once again, probably natural that greed can make dragons grow.
 
The same goes for Windigoes and their ways of squeezing out anger, hatred and bitterness from others, which they need to survive!
 
The Flim-Flam Brothers provided a valid service in return for the money they earned, and they build their machine using mechanical prowess, which - from what I saw from the show - is uncommon amongst ponies. They probably worked hard on it, and now, they harvested the fruit of their labor. Their mess-up with the barrels in the end is more likely to be because of haste, rather than sloth.
 
And finally, Queen Chrysalis needed the she couldn’t return to keep her own people alive. Sure, there may have been more diplomatic ways to gain this, after all, Princess Celestia and Luna are anything, but unreasonable - but considering the pseudo-medieval setting of the show, and the savage appearance of the changelings, it’s not hard to believe that they considered an all-out attack more easier than asking for help.
 
 
And finally, now that you’ve brought religionous themes into the show, consider THIS: we humans are imperfect. Sometimes, more imperfect, more corrupt than ANY of the characters, villains or not, we see in the show. Why should WE judge them for who they are and what they do, when WE had committed far more horrible things during our time.  
And we keep on committing them.
 
I know this is merely a theory you’ve drawn out, but I want to cut of the hypocritical theorizing before they even start. I hold no grudge against you, but keep in mind: anything you say is your opinion, so it may be biased to some extent. The same goes for what I just wrote.
 
All in all, don’t judge without reason.  
It’s a very human mistake, quite natural among our race, but it’s not something we should polish instead of abandoning the practice of it!
 
Nice theory, all the same. But keep in mind: there ARE counter-values.

Chrissy representing lust is always a concept I also use, when it comes to these sorts of comparisons, I guess it helps that she’s also technically a succubus of sorts. lol

@Fortune  
I’d say gluttony for shimmer. I think its more likely we get a villain that takes everything from Equestria or whatever country he/she is in.

Current update with the main villains, sloth and gluttony are unrepresented.  
Nightmare Moon is still envy, Discord still pride, and Chrysalis still lust. Now adding Sombra with wrath and Sunset Shimmer with Greed (although going with the definition of Gluttony as just “taking much more than you need”, you could make a case for that for her).

@Background Pony  
Still, Sombra would make for a better wrath than the Windegos.

@Dr_Robotpony
 
They’re antagonists.

Using the Flim Flam brothers, parasprites, grown up Spike and the Windegos seems like a real stretch.