I don't think there's any argument against Barcelona being the most successful team of the last decade.
Again, I think "decade" is a pretty arbitrary thing to define it.
In the last 8 years, since the Pep years - when they clearly were head and shoulders above anyone else, their results in the CL (again, the ONLY best-on-best competition, where you can't win a title by being inferior teams more consistently, you need to have a higher peak):
1 Win
3 Semis
4 Quarters
I'm sorry, but that's not the record of a team that's "CLEARLY above everyone else" in an era.
Not for me anyway.
I will say their record in the CL in the last 10 years is CLEARLY second best to Madrid. Both in titles and consistency.
But Madrid have the negative of only 2 La Liga wins in the last 10 years.
(total trophy count is closer because of all the Supercups and Cups which IMO are almost irrelevant in the big picture)
So, depends how you look at it.
I think it's silly to say either team has CLEARLY been this and that, "not even close" and all that internet jazz.
It's debatable. But Barca's CL record for a team of their quality and having a Leo Messi on it leaves a lot to be desired in the last 8 years.