I agree with this. Online poker sites charged significantly less rake than brick-and-mortar poker rooms. The same should be true with legal sports betting. Brick-and-mortar sports books typically charge about a 4.5% vig. I'd think that online sites should be able to get below that, but instead they're all up in the 10% range.
They spend an awful lot on marketing, but I would think that by far the most effective marketing would be a lower vig than your competitors. I could be wrong about that, but in the online era, word should spread very quickly about vig even without advertising.
I'm a big fan of the daily games and I hope that this genre of fantasy really takes off, but I think the vig is going to have to come down in order for it to survive long-term. At ten percent, the losers will outnumber the winners by too much, and a lot of people will get frustrated and stop playing.