When Guardiola took over Barca in 2008, that certainly was not the case. They were outclassed by Real in the league and finished the season without a title. He had a lot of freedom to make changes, because
Rijkaard´s way was not working anymore. He turned the team into the best of the world.
Now he is taking over the best. The situations are very different. Bayern was a perfect running machine in the last season, winning everything in a truly dominant fashion. He is basically trying to change a system (after announcing to only make "small changes"), when there is absolutely no need to do so.
It is of course understandable that Guardiola wants to make an impact at Bayern, but the expectations and also risks are higher now than 2008.