Jim Gavin just realised that you can't ignore the basics of defending against the other top teams when it really matters.
When they did their shortcomings were exposed & Gavin, bright man that he is, realised that if Donegal could frustrate them that a team like Kerry would too so he made the sensible decision & shored up the back.
Fair enough, it might take a bit of the sparkle off their flamboyant style but ultimately it will make them a better team.
I'm not so sure Muckross, there was a reason why Jim Gavin felt the need to move away from the Pat Gilroy template. I think that reason was the Mayo AI SF in 2012, were Gavin probably thought that 2nd half comeback was how Dublin should really be playing.
I accept he might feel the need to shore up a few weak spots, but I just feel completely changing the system is a bit drastic. Especially when you have a system that can completely blitz tight defensive units like Monaghan, a system that is very hard for every team in the country to cope with.