I think you understate what a big deal the decentralization was when Git came out. Back in the early 2000s, getting internet while out of the office was hard. 3G was in its infancy and expensive so you were at the mercy of finding a WiFi hotspot. Git's predecessors, such as SVN, were unusable without an internet connection to the server. Git (and Mercurial) allowed doing version control without an internet connection for the first time, which is a massive benefit for some types of development or doing work on the road. This aspect of Git definitely became less important as always-on internet connections became ubiquitous, but it's still super helpful sometimes. I can't imagine going back.
I think you understate what a big deal branching was when Git came out. Back in the early 2000s, branching was hard. Git's predecessors, such as SVN, didn't have branching at all until much later, and even then the implementation was riddled with problems and quite often the repo entered state where branches cannot merge back to main (which was called trunk back then).
No matter how beneficial the ability to work offline was, branching was still far more important. It's a completely different order of magnitude. Git without offline capabilities would still be a massive success. Git without branching would not.
