"he elements of gambling are consideration, a result determined by chance rather than skill, and a reward or prize; or, in other words, payment of a price for a chance to gain a prize. In addition, under a statute that prohibits gambling for profit, "for profit" is a necessary element of the offense. Thus, there is no "gambling" unless a participant is required to risk something of value."
Worldwinner.com a subsidiary of a US publicly traded corporation has progressive pots that payout based on the number of entries and they charge per entry. They argue that all their games are skill-based and lack the element of chance necessary to be legally considered gambling. Obviously just having skill as an element of a game would not make a game not gambling, after all poker involves skill. There needs to be no element of luck. WW addresses this by having players play the same exact same game against an AI and then the winner is the person with the best score. Other skill based games sites have done it the same way.
If you remove the wager element it's also not gambling. If the particpant is not risking something of value it's not gambling.
WL could easily rig up a single player tournament against AIs where the winner gets the prize and that would not be considered gambling if it involved no element of chance. Or WL could offer a zero luck competition similar to a chess match (which is not gambling even if played for money).
There's also the argument that a discounted or free "membership" would not constitute a reward or prize because it has little inherent value. It's non-trnsferrable and costs next to nothing to WL. I realize one could argue that buying a membership from WL costs $29.99, but that's not the same as offerring $29.99 as a prize. This is a weaker more subjective argument.