Yes, it's not hard to do. Marry an American and it will take much less than 9 years to get a green card, if you want one.

What if one is already married? Or in a relationship with a non American?

Then it is subject to the same bottleneck as described earlier, which is greater than nonzero.

I'm not OP or GP, but that was my interpretation.

I know. I am criticizing OP on suggesting that it is not hard to immigrate to the USA. As if it is even a worthwhile option to suggest that people leave their families and marry Americans.