#4 Part-timers serve a larger logical purpose
With Shawn Michaels returning to in-ring action and The Deadman staring down his path, there's little doubt that the two will square off at The Undertaker's birthplace. In 2016, Undertaker declared himself a SmackDown guy, though he ended up participating on RAW after. The Undertaker will always remain synonymous with Smackdown, as Shawn Michaels has been to RAW.
It would thus be fitting that the two legends of their brands face off on a PPV all about brand supremacy. Removing the part-timers from the whole equation and then letting them main event, just diminishes the purpose of the exercise. Yet, placing stakes of brand legacy into the mix uses the part-timers for a better purpose.
It'll also let them mix it up with the other stars on the road to Survivor Series, just imagine Finn Balor stopping the Undertaker or AJ Styles hitting back at Shawn Michaels. Lastly, it will showcase that nothing is above the product and brand.
Also, who doesn't want to see Undertaker represent Smackdown, he owes it to the blue brand even if Vince weirdly doesn't like it.