I can only speak from personal experience- i pulled my first legendary (a decent one) before i had bought anything, and i have only ever been a minnow (tiny spend). My luck on my new account has been terrible however.
Some whales will throw thousands at the game, that means for every shard you open they might open 100 or even 200 shards which makes it far more likely they will have the top champs.
I do believe our in game actions are logged and it influences the packs etc that we see. But it is not in the interest of plarium to give FTP no legendaries at all... they want you to spend and that is far more likely if you get a decent champ you want to invest in.....
I got frustrated at not being able to pull a decent second poisoner and had dramatically reduced my playtime.... theni pulled draco which then led to me playing again and getting the 10 quid gempack for gems to help level him.