It's not just Westerners who would tend to see Shen Wei as the bottom--unless things have changed in the last decade, Japanese seme/uke rules are hard-coded for him to bottom, what with being The Shorter Man.

Do you know if Chinese BL fandon uses The Height Rule? Or do they have some other Rule?

And the first slash discussion on record is in The Symposium, where Plato and his fellow fanboys sit around, drinking, and talking about whether Patroklus topped because he was "the older man" or whether Achilles topped because he was "the greatest warrior" (the possibility of switching doesn't seem to have been on the table).