I think an underatted team was Ac Milan from 2003-2007, they had a lot of talented players. They had such a great defense and offense. They had superstars all over with guys like Pirlo, Gattuso, Nesta, Cafu, Dida, Kaka, Shev,Crespo. Spain struggled against Italy a few times (2008 and 2012) which shows that Italian football style would have been an issue for Barcelona if they faced them more often.
Gegenpressing spelled the end of tiki taka. Heynckes’ Bayern, Pep’s City, and Klopp’s Liverpool (probably his Dortmund side too) would all have given Pep’s Barca a serious test - not because the players are better, but because the system is designed to compress teams that like to pass into making a mistake.
Before that I’m less sure. Probably the best team I’ve ever watched, I felt like I was watching a team that had “solved” football.
i wonder how the 2011 final would look if it was shalke vs bayern.