Which would be a far more impressive counterargument if over half the Vertigo titles took place in the shared DC universe alongside Swamp Thing and Sandman. Most of the titles have been stand alone series where the Justice League doesn't drop in for cameos (Preacher, 100 Bullets, etc.). Moore's run on Swamp Thing clearly influenced Gaiman's Sandman (as well as just keeping him connected with comics back in the day). However the Vertigo imprint started in the middle of Sandman's run (1992) and Moore started his Swamp Thing run back in 1984. I'm pretty sure he was off on other things by the time Vertigo was launched. I do know that Sandman was considered the flagship title for Vertigo from the start of the imprint to the end of Sandman's run, while Swamp Thing seems to have been grandfathered into the imprint due to its connections with Sandman. On top of that, the half dozen or so Vertigo titles that take place in the shared DC universe are either direct spinoffs of Sandman (The Dreaming, Lucifer, Sandman Presents) or Neil prompted titles (The Books of Magic, The Books of Fearie), which suggests that Sandman's influence on the field was stronger than Swamp Thing's, despite the latters influence on the former.
There, caused my trouble for the day. Enjoy.