I don't think we need to worry about Alex Ross' career.
That said, I find the more time passes, the less interested I am in his work. For a while, I thought, "I wonder how he'd draw [insert character name here]," and that kept me coming back for more. But now that I've seen his versions of pretty much every major DC and Marvel character, there's not much to keep me interested. I just don't see enough variety and inventiveness in his layouts and poses to keep things exciting.
I love "Mythology" as a sort of album collecting Ross' take on all the DC big guns, but it occurs to me this "album" approach is much more enjoyable, in the end, than any of Ross' "comics" (Peace on Earth, War on Crime, etc). For me, the true geniuses of comics are guys like Eisner, Cole, Kirby, Sprang, Gil Kane, etc...guys who remained unpredictable and innovative throughout their careers and could always surprise you with new ways of telling a story, visually. Ross, in contrast, does nice majestic poses but there is rarely that sense of energy, enthusiasm and giddy chaos I associate with true "comics" (as opposed to pretty, painted panels).
Actually, I find some of Ross' pencil work more intriguing than his finished works, and almost wish he'd put away the paint brushes to try a new career as a penciller.
And I don't have an issue with Superman's muscles. If anything, what bugs me about Ross' Superman is the same thing that bugged me about Bama's Doc Savage...he looks about 65 years old!