Yeah I wouldn't say Denzel is over-rated....in fact I've never heard anybody ever say that before. He does have his own style of acting and all his characters tend to reflect that style but he is a very good actor. Tom Hanks isn't overrated either, in fact I hate that term "overrated" when talking about actors. It's a matter of taste and preference.
The man should never have won an Oscar for Training Day...it just wasnt that good of a performance. He's no hack, but he's average at best.
As for Hanks...i'll never understand the appeal. Dragnet, good. Castaway...worst movie EVER!