Yes, though I do think it's important to emphasize that they're taking the exact opposite strategy for this release -- like, for example, they fired all the management from their digital team and hired MMO veterans to build a brand new studio from scratch.
Probably not. 30% is way too big of the revenue margin to give Steam for free. MTGA is going to be marketed heavily, I don't think that the exposure gained from Steam is anywhere close to the 30% loss in revenue.
Magic Duels was a promotional game, it was a gateway to other MTG products.