Check-out the 1993 and 1994/95 series' (the only ones where fair comparison can be made as they're the only ones where both played in a fit state to do so - Slater missed 1997, Atherton wasn't fit to throw a bat downhill in 1998/99 and both had declined and were poor in 2001) and you'll get a better impression of the relative capability of Slater and Atherton. Even that's not entirely fair as Atherton was facing McDermott, Hughes, Reiffel, Fleming and Warne and Slater was facing Ilott, Bicknell, Malcolm, McCague, Such, Tufnell et al.
Rating the two by how they performed against other teams is rather fairer.
As for Taylor I don't have any real problem with somone considering him superior to Atherton as he was a damn good batsman but as I say, personally I don't have a lot between them.