I don't believe the issue around small numbers of players making all of the money is important. As someone who uses both platforms for fun, I find I'm willing and many of my friends are willing to lose a bit of money each week as it makes the games far more entertaining to watch when you have a rooting interest. Many of the sports leagues and ESPN realize this which is why you saw them invest in these companies. Fantasy leads to more engagement with the sports and daily fantasy leads to even more engagement.
Daily fantasy is not for everyone, but it'll likely maintain a core number of users, many of whom use both FanDuel and DraftKings. Acquisition costs will be less important in the future and provided that fixed costs such as legal fees decrease in the coming years, these companies will become stable and profitable.