Where do you rank Edwin Valero?

Top 50, definitely. Top 30, maybe but not any higher.

He beats guys like Corrales, Katsidis and Castillo who some people have in their top 30 but he’d struggle against counter punchers like Whittaker, Marquez, Mayweather Jr. & Moseley. I think he’d fare better against a boxer-puncher like Durán than those aforementioned.

 

I think there's something off with the second paragraph - I can't really grasp the final point of it - but yes, my argument is that being 8-0 in title fight counts for nothing without a context. Fight being contested for a world title does not automatically makes a win any better. WBC can sanction something like Canelo against Matthew Hatton as a World Title fight and then Canelo can fight Erislandy Lara in non title fight because He can't be bothered making weight or paying sanctioning fee.
Tua beat better fighters in non-title fights than Mosquera did in title fights. Tua's WBC International title "reign" was superior to Mosquera's WBA Full title reign and probably superior to either one of Valero's title reigns also.

Relatively better than Valero's opponent's - and certainly better than Mosquera's opponnets (I responded to Your comparision of Tua and Mosquera). Noone of Your nitpicking changes that, same can be done for Valero.
Mosquera was lucky to get a win over gate-keeper in Argentina just before losing to Valero - DeMarco was never seen as an elite fighter either. He needed heroic late comeback against Linares, who looked level above for most of their fight. He could not compete with Broner.

To me it does, yeah. Valero has 2 wins over genuine world class fighters - Mosquera and DeMarco - and perhaps one borderline, in Pitalua. I don't see any point of talking about his defences against shot featherweight gate-keeper Velazquez or some local Japanese guys that had no bussiness fighting for world title and only got a shot because Valero could not fight in the states and Japanese promoters could put some money up to organise a fight. Those are the type of opponents that prospects can fight on the way up, those are not championship level fights whether someone sanctions it as such or not.
Beating Byrd and Tua far outweights anything that Valero's done in his career.

 

Then we'll just have to agree to disagree.