I think the people believing the monetization model wasn't the problem are way off. Nobody I know, including some card game enthusiasts, gave it a second look when they found out you have to pay for the game and then pay for more cards. Twenty bucks to try something I don't understand, more if I like it? Super ultra hard pass. So I'll say right now I know very little about this game specifically and based my views on it largely on psychology and gaming trends.
Targetting the hardcore crew directly is always challenging with this type of thing. Hardcore players aren't just born that way - they were just normal players that liked a game enough to start getting into the specifics; researching mechanics, watching streams, and otherwise becoming quite good through a natural, evolved process. By not allowing casual players to get in because of the money gate compared to their competitors, they made it too easy for these hardcore fans to never emerge naturally. You have to WANT to be a hardcore player to pick something like that up, and it sounds like a lot of players just simply weren't interested.
And really, who was this targeting again?
* If you like Dota 2 then you're likely to be playing Dota 2
* If you don't like Dota 2, then the themeing is likely a turn-off to you. Maybe your experiences with it, or Dota 2 players hasn't been positive. That combined with the cost of entry means that people were likely to get their card game fixed in less starting-player unfriendly ways, which is exactly what happened.
20/20 hindsight and all but I said this on day 1 of the reveal so I'm not nearly as shocked as the others that seem confused its failing.
I think the only reasonable way forward is to make the initial experience ftp. Costs nothing to download the game and play modes. Maybe you can only play the mode where you get to keep your cards a couple of times a day. But the thing would be that you couldn't trade in the ftp mode. You could grind for cards if you wanted to over enough time, but if you ever wanted to just spend the few cash to specifically target the few you need on the marketplace you pay the 20 bucks to upgrade the account. I think something like that would be a good compromise - it lets players that aren't going to be happy self-weed out, and makes sure the people that do want to stay will participate in the economy. If there are better ideas other than 100% ftp cosmetic stuff or just letting it die I can't see them from the outside.