I've been on vacation these last few weeks, so I couldn't respond.
1. No, I never bashed Justin Upton last year.
2. I don't focus on batting average. It's prone to too much flukiness because of BABIP. Maybin's is over .400 which is absolutely, unquestionably unsustainable. He also grounds out 60% of the time and has barely a 10% line drive %, and less than 30% of his hits are XBH. Those four peripheral numbers along with (BB rate - where he's very strong) and K rate (where he's putrid) tell much more about a players performance and development than looking at batting average.
3. Working off the assumption that his numbers will improve as he moves up in levels is completely illogical. It's a harder level, and therefore it stands to reason he'll do worse against better competition. Sure, some may do better, but it's an anomoly. You can't cherry pick people and think that it's a pattern.
4. The only things Maybin has done which can be reviewed positively is overall speed/defense (where he's good and there's no reason to think it won't continue), plate discipline (where he's good and it should also probably continue), and batting average (which absolutely isn't sustainable as he moves up the ladder - debating that fact is ignorant of sabermetrics and is merely wishful thinking
5. Even in your bull case looking at his batting average - he's still not showing much power (and what little there is, has been declining this year) and strikes out a ton. He just hasn't done anything really good over the last two years, while there are other prospects who have dramatically outperformed him.