The "big stack conspiracy theory" has existed forever, and some people feel this way about every single online site, which has existed. Its largely fueled by confirmation bias. As humans we tend to remember bad outcomes more than good ones, and since its per definition always someone with a bigger stack, that busts us from a tournament, its not difficult to see, where this idea is coming from.
In top of that big stacks are supposed to play more lose near the bubble and on the final table, so statistically speaking we are more likely to be all-in against a big stack. And they are more likely to hold a relatively marginal hand, which they can "suck out" on us with, because thats basically just them playing good poker.
If for instance we are in big blind with a 12BB stack on the final table, and it folds around to small blind with a 45BB stack, its totally reasonable for him to move all in preflop with any two cards to apply ICM pressure to us, especially if there are other even shorter stacks at the table, which we need to try to outlast. And when we eventually do call him with AK, his 72 has 32%
equity. So one in three times his junk hand will bust us from the tournament, and this is when, the tilt and conspiracy theory is fueled.
The solution is to learn the equities and truly understand and accept, that AK is supposed to lose to 72 one in three times. So when it happens, its not a sign of the
poker site being rigged. Thats like saying, that if you roll a dice, and it comes 1 or 2, then the dice is rigged. A completely ridiculous statement, that noone in their right mind would make.
The next step is to learn tournament strategy including push-fold, so that you know, which hands you are supposed to call or jam with short stacks, and so that you better understand final table and bubble dynamics. Often the underlying issue is, that people play to tight and passive, and therefore they often end up as the short stack being "bullied", while they wait for their AK or their big pocket pair to finally make a stand.
And this is basically not, how you win poker tournaments or even achieve a high ROI. What you want to do, is to adopt an aggressive and sometimes fairly loose play style, so that more often you are the big stack, who can push other people around. And so that you can afford to sometimes lose one of those unavoidable coin flips. More on confirmation bias in the video below.