Certainly the acid test for any defender who wants to be considered amongst the best of all time is how they have fared against the absolute best. I take your point about the calibre of what Rio and Van Dijk have faced, although I don't think the margin between
@Righteous Steps list and what Rio has bossed in his time is that wide. The best attackers in the world around 2004-2008 would be Henry, Shevchenko, Kaka, Drogba, Eto'o, Torres and Villa. Arguably they're a bit better than what Van Dijk has faced, but equally Rio didn't always come out of those encounters covered in glory either.
Of course earlier in his career he faced Real's Galacticos which included post-injury Ronaldo and didn't really handle them, so I don't think that works in his favour. He helped shut down Rijkaard's Barcelona in 07/08 with a very impressive display, but a central Messi scored winners against him in 2009 and 2011. While over the course of his career he's played against many of the greats, I don't think he's dominated the best forwards of his generation any more than Van Dijk has in his. While rating Rio very highly, I think - like Van Dijk - his CV is not quite as strong as Baresi, Nesta, Scirea, Figueroa, etc in shutting out the greatest of all time.