The fact that some particular people are aware of how marriott does this and know to look for it doesn't show that it's not deceptive. To the contrary, actually, the argument that "well if you know where to look you'll see the actual pricing" adds weight to the claim that the way marriott is doing it is deceptive.
The use of the word "FROM" says it all. I agree it should show the average nightly rate or a total below the rate for all the nights.