shogun didn't looked "gassed" until the third, and gustafsson took him down in every round. also, you could probably attribute shogun's fatigue to the incredible amount of punishment he was enduring.
you're right that alex hasn't shown awesome single or double leg td's, but he's so creative with the way he transitions from striking to grappling, and getting the td when it's available, that i can see him hip tossing anderson or tripping him then getting on top and doing some damage.
the fact that he managed to get some significant gnp on shogun is also impressive. rua has shown the ability to get up vs anyone who's taken him down, and his bjj off his back is leagues ahead of anderson. the best silva could hope for would be to wrap the mauler up and hope the ref stands them up.
He didn't really do anything to Shogun on the ground honestly.