I don't know why you say this. Hasbro even made a Powerpoint of what they see as Magic's brand strategy going forward that includes their plan for MDN to sunset MODO/Duels and their view of eSports and online viewership as one of the key future pillars of the brand:
http://www.purplepawn.com/2015/11/magic-digital-next-in-development-by-hasbro/
It's relevant here only inasmuch as Hasbro reveals more about their medium-to-long-term strategy publicly than a privately-held company typically would because it wants its shareholders to get excited.
Right, I don't think there's an equivalent of
this for IsHearthstoneStillBad.
Yeah, because they absorbed a giant new growth market. Magic has something like 10x as many players now as it did for most of the 2000s, it's natural for that growth to taper off at this point. Plenty of people in that expanded market don't play MTGO though, since clearly that hasn't had the same type of userbase growth.
I don't think you shouldn't assume either. Think about it this way: out of the 12 million Magic players worldwide, some small number (let's call it 1m) actually play Magic Online. If you can add another 1m users from that 12m by launching a new product, while only burning 250k of your existing userbase, that's an enormous boost to your business.
The way to do this isn't to do exactly what HS is doing (because Magic can never be as good at being Hearthstone as Hearthstone is); it's to look at more general areas in which HS is successful and find ways that Magic can improve. Like: HS gets a ton of promotion from streaming, while MTGO is ugly and hard to stream well; creating a new client with a good streaming interface could add a lot more player interest. HS is a game you can download for free and play infinite games, plus earn cards slowly over time; a core Magic product with an account shared across devices (like MTGO) that had a model of this type (like Duels) could pick up a ton of new players just by avoiding upfront expenditures. Hearthstone cards are cheap and feel like good value while MTGO cards are a far worse value than paper ones; eliminate redemption and you can suddenly change your pricing model to solve that. And so on, and so forth.