My friends and I have acquired some of the recent duel decks over time — Heroes vs Monsters, Zendikar vs Edrazi, Elspeth vs Kiora, and Speed vs Cunning.
We've tried each of them a few times, and while I'm pretty satisfied with them, some of my friends are coming out concerned that one of the decks in the pairs we've tried might simply have a greater chance of winning than the other. For Zendikar vs Eldrazi they're thinking the Eldrazi has a moderate edge; for Heroes vs Monsters they suspect Heroes have a strong advantage.
This might just be our limited number of games, who was inclined to play what, confirmation bias, etc. Trick Jarrett won with monsters 3-1 for instance, and I imagine duel decks are at least intended to be even. I haven't been able to cue Google to offer up an answer as to the odds of each deck of winning.
So, I need to turn to your expertise and shed some light that might either confirm what my friends suspect or assuage their concerns.
Are all duel deck pairings intended to have a roughly even chance of winning against each other? I'm assuming this is the case, but that's just me assuming. More importantly, do they actually tend to work out that way in practice, or are they known to sometimes come out with a strong bias toward one of the decks?
I would prefer to see citations from credible sources about developer intentions and win rates. (Official sources like the Wizards development team are credible. If there's genuinely no citations available, I can accept that, but I'd like to be informed of that.) It's pretty reasonable to assume that something called "duel decks" would be intended to have even chances of winning, but I don't want to go by assumptions — and I want something for my friends to have confidence in. It's possible they have design time constraints that prevent them from really achieving evenness, or that the product's seen as secondary and 70/30 odds is considered good enough, etc. It's more probable they want everything to be 50/50 (or 55/45 at worst) and have plenty of resources available and devote themselves to successfully achieving that every time, but I'd like to know that.