Claims like this are in my opinion just nonsense. Sure sometimes you see a bad player on a heater build a huge stack. Which they then often give away again without finishing in the top 3, where the bulk of the payout is concentrated. But other times you are on the bubble or at the final table with a middling stack, and the short stacks just keep on dubbling up to survive and drag the process out.
Also what would even be the motive for poker sites to rig their RNG to favour a big stack? The typical explanation is to make people bust faster, so they play more tournaments. But come on guys give me a break. Plenty of people play turbos or hyper turbos anyway, and why do you think, 888 keep on promoting their BLAST games?
888 also offer several tournaments, which are still very favourable rake wise. They have 2,2 and 5,5$ R+As, where only the initial buyin is raked but not the rebuys or addons. They have 4$ knock-out tournaments with only 30c rake. They have a daily 7,5$ bounty builder with only 50c rake. They have "rake or break", where the rake is refunded, if the tournament does not reach its target.
Can you imagine the board meeting, where someone suggest "lets rake the rebuys and add-ons in all our tournaments and make the 7,5$ bounty a 7,7$ to bring it in line with our other tournaments". And then someone else reply "nah lets rig the RNG instead and get the suckers that way". Its just comical to even imagine something like this.