But the Orange line still terminates at PSU, and it also sometimes becomes the Green at PSU. You also don't have to stay on the train past city center, and Steel Bridge raises don't affect the intended Orange Line service to and from city center; trains just circulate at Union to minimize delays.

That's by design, which is my point. The Yellow and bus lines across the Steel are always affected more than the Orange line, and the ability to terminate at Union on a bridge raise allows for bus transfers over other bridges—it's integrated to play to the strengths of combining bus, streetcar, and LRT, and minimize the weaknesses of the Steel bottleneck. It's also why it's not just a Yellow line extension south.