In bridge, are the two "equal vulnerabilities" basically equal?
The equal vulnerability is only talked about at game level or higher. I haven't heard it being used for partscore battles, where it does not make too much sense, as you say.

Playing matchpoints, in partscore battles, the deciding factor is whether you are vulnerable or not.

-100 (down 1 double, non vul) might lead to a great score, but -200 (down 1 doubled, vul) is usually a poor score at matchpoints.