Almost everyone is a let-down compared to 2004-2006 Santana, but yes, I'd say he was the last true ace. Liriano could have become one if the coaches would have altered their approach with him (look at how he's thrived since arriving in Pittsburgh).
Bull ****. The Twins overpaid for a couple pitchers who are mediocre at best. Hughes and Santana have career ERAs of 4.33 and 4.16, respectively, both of which are below the average ERA for starting pitchers this season. Those two guys would be lucky to make the playoff rotation for any of the contending teams this year.