Wacker was the person Marvel wooed away from DC as he was doing the weekly Countdown series a few years back.
Most of what you say is correct, but I have to correct you on one thing: Wacker had nothing to do with the train wreck that was Countdown; rather, he went over to Marvel part-way through the run of 52, which (in my opinion anyway) remains the gold standard of weekly comics.
I'm not surprised that Marvel would end the thrice-monthly Amazing if Wacker doesn't have time to do it; there's no one else I can imagine who'd be able to take charge of such a difficult task.