You’re right, it wouldn’t be possible.

I’m in Taipei now, not every intersection looks like this. But I remember seeing it at Chiang-Kai Shek Memorial Hall station (https://en.wikipedia.org/wiki/Chiang_Kai-shek_Memorial_Hall_...). On the Taipei MRT map you’ll see that both the red and green lines make a change in their trajectory here, allowing them to go parallel.

I think the technique the OP described is “necessary, but not sufficient” for these types of transfers.