youdontknowme One, the US two-party system means that the largest party automatically has a full majority
However nothing in the US constitution says that it has to be a two-party system.
In an imaginary world it could well happen that most conservative democrats and the non-trumpist and a bit more progressive republicans join into a new middle field party. Nothing would stand in the way of this happening.
With partisan rules you are right. The speaker of the house has the right to bring bills to the floor of the house for a vote (or not to do so, effectively blocking legislation). While many scholars and I would consider this an abuse of the position, it is within the power of the position and has been done over and over again, yes.
I was not trying to state that German and US political systems are completely the same with just different names. I was simply trying to help a young person to get a better (but admittedly still incomplete) understanding.