Also, submitting thousands of entries does not tilt the odds in their favor. It tilts the odds against them for a lot of reasons. And it takes way more work. They do it anyway because entering thousands of contests with an 8% ROI is more profitable than entering five contests with a 30% ROI. But please don't fool yourself into thinking that their ROI goes up with additional lineups or contests entered. It's the opposite.
By the way, those numbers aren't completely made up. It's pretty easy to get around a 30% ROI if you use pretty basic tools and enter just a few contests a week.
In the FanDuel contest exclusively for Footballguys subscribers, for example, the average entrant has a 24% ROI (including the value of tickets to the Week 11 contest with $40,000 added). So just enter that and be average, and voila, you have an expected ROI of 24%. At smaller sites, it is not all that difficult to find overlays that offer the average entrant better than 24% -- I regularly see some where the average entrant has an ROI upwards of 50%.
In contrast, maxdalury, who is probably the very top DFS professional right now, has said that he has about an 8% ROI, on average.
His huge disadvantage is that he can't just cherry-pick the contests with overlays. To get as much money into play as he does every week, he has to play a zillion contests where the average entrant has a -13% ROI. And he's not just using his very best lineup. He's sometimes using his 30th best or worse. (I don't know how many lineups he uses specifically, but I've been known to use my 100th best lineup.)
It's actually
harder for the pros than it is for the hobbyists. But they compensate by spending way, way, way more hours per week at it than the casual hobbyist does. That's where their advantage comes from.