To be fair, those comments about Messi were pretty stupid. Not only has Messi been stopped numerous times, but portraying that kind of defeatist attitude helps no one. Look at what Heynckes said before the clash in 12/13:
April 12, 2013:
Bayern's confidence shone through in those games. Of course, the teams and situations are different but what the coach says does matter. And from what I've heard, the Bayern players did not take too kindly to Pep's tactics or words.
I agree that he should not have made those comments about Messi for they provide ammunition to those inside Bayern who want to criticize/scapegoat him. Other than that, what people say before games matters very little, if at all.
In his stead, I would just fuck off to Man City, especially if they could spend big this summer:
a) Winning the BuLi with Bayern is merely par for the course, there is not credit to be had out of it. Winning the EPL with City is however a success.
b) Reaching the semis with Bayern and losing, is considered a big failure by Bayern supporters/German press. Doing the same with City will be seen as a success. Anything better than that, and the English press will deify him a la Jose.
c) He will have more control at City.