I know we're all boarded the Trout hype train by now... but I seem to remember the Heyward, Hosmer, Lowrie, etc. hype trains all leaving relatively recently too (and let's not forget about Strasburg's lost year). Even Ike Davis was lighting the world on fire last year before he went down. Just sayin'. A lot can happen in a short amount of time.
In hindsight, I probably went a little overboard analyzing his statistics, and I'd still probably think Kemp and Cutch may be rated higher than him going into next season, but they don't have the upside of Trout. I think we know what Kemp and Cutch's ceilings are, with Trout, I don't think you do at this point.
His WAR is 5.0 at the moment, for those that take an interest in that stat.
McCutchen's .372 AVG is unsustainable. He'll come back to Earth at some point.
As for Trout... I can get steals elsewhere and I'd rather have more reliable power from my early round picks.
Ryan Braun and his 61/26/65/16/.312 stat line are saying HI.
CarGo and his 62/17/60/12/.331 stat line say WASSUP.
Josh Hamilton and his 55/27/76/6/.301 stat line are feeling left out.
...and there's a whole host of other guys I'd rather have over Trout next year in the 1st or 2nd rounds where he'll probably be taken.
But I think you've seen what the best season from those guys.. If he finishes the year with say a .320 AVG, 100+ Runs, 20-25 HRs, 70+ RBI, and 60 SBs, I'm not sure there's a better player to have in a roto league, given the all-around production. What hurts him is he plays the OF, and all those guys you mention are OFs, but he's got a shot to lead the league in BA, R, and SBs as a 20 year old in a partial season. In roto leagues you're looking for balance, and for the advantage Trout could give you in those 3 categories, He's not putting you completely behind in HRs and RBIs.
I think a viable case can be made, and I generally agree with you that grabbing power early is key, but I just think this is such a unique player that it needs to be considered.