I don't want to get into ref decisions from 2009-11 because there were many decisions against Barcelona that, conveniently, aren't mentioned as much as the ones that went our way. Quite normal I'd say, because everyone hated us back then and wanted to see us get beaten.
The Pep Barca team and cycle ended in 2012 when Pep left. I see no point in discussing what happened after. Some of the key players declined. Puyol was gone, Abidal had health issues often, Xavi declined a lot as he was 33 and his role could not in any way be replaced, David Villa was never the same after he fractured his tibia in late 2011, and he was also in his 30s. Alves was on and off (in fact his crosses had become an inside joke here on the forum) And Pique only produced one elite season after 2011: 2014-15. More like half a season in reality, and that only after Lucho decided to bench some sense into him.
And since Barcelona is a fucked up political club, Barcelona never had the chance to rebuild under Pep, like most EPL sides do. Under the same leadership and following the same principles. Some journalists that were close to Pep hinted at the time that Guardiola wanted to remove some big names that lost motivation. The board overruled him and sided with the players. This makes perfect sense to me.
Anyway, the fact remains that 2009-11 Barcelona team set a huge bar to beat in terms of titles (both club and national team level as the platform from Barcelona was fully adopted by Spain), playing style, domination vs rivals, legend status. All mixed into the same winning formula.
That aside, of course top class current teams will appear. We have City, Liverpool, current and past versions of Madrid, past versions of Bayern. And so on. All of these would've been hard games for any side in history.