he may not be clear-cut #1, but he's a guy you can share the #1 option with. him and yao can switch 1a/1b. manu was never good enough to be a 1 option. he's at best a #2. hell on most nights, he's #3.
What is so terrible about using T-Mac as the second option behind Yao? Yao at least can convert at a better than 50% rate. In single coverage he's probably the toughest job for any defender in the entire league?