RNG always has variance. You can flip a coin 1000 times and chances, all things being equal, that the count of both heads and tails will be within a margin of error. So to use that same example as an analogy, it's like you're flipping a coin for every card in the deck, then every player at the table and probably more on top of that for good measure. However, irrelevant of how many coins you have to flip, the results will still always come out at about equal - within that same margin of error based on the sample size. The only factor left is time; how long it takes for that variance to even out.
Nobody can be sure as to how the online system works because it's a closely guarded secret - However the tin foil hat in me
tells me that I wouldn't put it past a big business to weight the decks a certain way to entice more action, thus increasing pot size, thus hitting their rake cap more often, but I don't think they would specifically rig the game to make a certain person, like the big stack at a table, lose more often.
In on demand, no buy-in
freerolls. All gloves are off, Nobody is paying for anything and I wouldn't put it past them to keep track of players entering and ensure they don't win too much free cash. But this is just the tin foil hat in me and can probably, most likely, maybe, be safely ignored.