I agree with the Parabellum, and will also add that you were correct in not "fighting for the controls." When the captain says he has the controls, it's not your place to "fight" for them because you don't have a right to them.
If the flight is entering an unsafe condition with the outcome of the flight jeopardized, then speaking up is warranted,and if the captain is unresponsive, then taking control is an option. But when you're already unstabilized and have entered the approach with poor airspeed control, lack of configuration, and it's only getting worse, at some point the captain has a right and a responsibility to take it away.
Sounds like you were far behind the airplane, it wasn't helped by the captain accepting a base leg (perhaps he could have made it work out, but you weren't ready...that's a communication issue). Sounds like the captain was farther ahead of the airplane than you, and elected to leave you behind the airplane while seeking to make the approach work.
While his actions go against the grain of the traditional stabilized approach, he was stable to 300' per your description, having salvaged a bad approach. A go-around is usually the best thing, but perhaps his biggest mistake was failing to take the airplane away a little sooner.
You could say the captain made big mistakes, but one of them may have been placing too much faith in you. Again, a communication issue; next time, be sure to tell him you need more distance and time, and next time, slow down sooner.