> Two years ago in my "State of Design" articles, I said we'd let complexity get a little too high. Last year, I said we overcompensated and ended up with complexity a little too low. I'm happy to say that we've found the middle ground and have been producing sets that seem to be hitting the sweet spot.
> The key to this success seems to be us towing the line of complexity at common, but upping the amount of complexity we allow at uncommon. This allows us to take in-theme things for the set that would normally be rare and pull them down to uncommon to allow us to raise the as-fan of the theme. A good example of this would be the planeswalkers in War of the Spark. The uncommon planeswalkers, in a vacuum, would probably be rares in a normal set, but by allowing ourselves to lower their rarity, we were able to infuse War of the Spark (especially Limited) with the planeswalker theme.
> Another component that allowed us to pull this off is a willingness to be more aggressive with the power level of commons, especially answers, to help make them more relevant without having to up their complexity.
( https://magic.wizards.com/en/articles/archive/making-magic/s... )
The power level of commons was long one of their primary defenses to the question "why do you print bad rares?". Combining the introduction of Mythic rarity with the axing of staple commons did terrible things to the balance of power across rarities. As alluded to in passing here, they seemed to believe that powerful commons made the game more confusing to play and/or less fun, hurting their potential market.
You can track the issue on Doom Blade ( https://gatherer.wizards.com/Pages/Card/Details.aspx?multive... ). In M12 (2011) it's a common. In M13, as part of their commitment to continuously rotate which cards fill which roles, Doom Blade is replaced by Murder ( https://gatherer.wizards.com/Pages/Card/Details.aspx?multive... ), which is also common. In M14 (2013), Doom Blade is back! But it's an uncommon, where it stays for the next several years while they publish articles about how their new philosophy of design means you shouldn't have broadly useful removal at common for under 5 mana. But between M19 and M20, Murder shifts from uncommon to common. Murder is still much weaker than Doom Blade. But the philosophy of "no common removal unless it's either intensely situational or too expensive to play" has disappeared.
They're trying to balance money extraction, player demand, and the broader health of the game ("after playing 20 games, do I still like this?"), and feedback on those three issues has very different patterns of immediacy and accuracy. (And, of course, money extraction and player demand are in direct conflict with each other.)