From a lore standpoint, you should not be able to QSS Urgot's ultimate.

Urgot's whole shtick is that he values power through will and strength rather than through corruption and money. Only things built into champions's kits should be able to stop Urgot's ultimate. Things like Gangplank orange, Kindred r (when both in the circle), Kayle R, and Tryndamere r should be able to stop Urgot's ultimate, because it shows the true strength of the champion. QSS is a purchased item. Power through money goes against Urgot, so they should be judged as unworthy and be able to not use the item on ultimate

Thank you, I'm ready for the downvotes.

Edit: 5 downvotes in less than 10 minutes. About what I was anticipating.