Theyll probably spend enough money to make sure they don't decline. They have barely spent much over the last couple of seasons. I do agree with your point in general though. We just have to take a look at Barca who haven't had a smooth transition since the Xavi and Iniesta days
I think Barca are gonna have a hard time in the coming years, Messi getting older, Suarez getting older, mediocre midfield (looking at their usual standards the last 10 years or more), and the loss of Neymar.
Was it you who said PL will be on the rise again? I kinda agree with that. They have the money and its all a cyclus in football.
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It's funny to hear a Bayern fan say they need to rebuild heavily when the situation for Bayern is not as critical as Juve's

Try being a Juve fan, our midfierld is ruined, our defence is so far away of what if used to be, and a lot of veterans are leaving
The thing is Ribery and Robben have carried us to so much succes, so it will be hard to replace them 1-1. Coman is doing an excellent job, but is out with an injury and then we get Gnabry in who had a great season for Hoffenheim.
None of those two are world beaters, but well Bayern fans gotta put their faith in both. Maybe we will go out with the big wallet in the summer and look for yet another world class winger, I would be glad.