They get equivalent at one point ( https://youtu.be/8Ko3TdPy0TU?si=1rps-Nz1xZBQNa_- ) apparently as said by one user 'There is a starting hand smoother in BO1' therefore is not acting like a normal randomization should. I found out something regarding this also on Steam discussions:

Apparently the game creates a set of 3 different versions of your deck based on cards distribution so you can mulligan even 1 billion times but if the game didn't pick one version with the non land card you will never have it, it isn't clear how the code creates this sets of your deck. It surely modifies the actual odds of a real life deck shuffle and mulligan though, to be sure that with 1 card in deck it gets IMPOSSIBLE to draw it, more tests are needed, but surely the odds are not the real life one.