Regardless of which on you create the content on, assuming they all federated with each other correctly, every instance hosts its own copy of your posts.
Standards are good. What's not good is that Google controls the standards.
Open source or not, Google currently has the ability to dictate web standards as they see fit.
Why? There are 2 reasons:
Chrome has a 63.55% marketshare (as of the time of this writing) of all web browser usage
Maintaining your own fork of Chromium or even your own separate browser engine (Like Firefox does) is extremely difficult.
There's a reason so many of these browsers just use Chromium. It's because Google is doing the Lion's share of the work. Modern web browsers are some of the most complicated pieces of software ever written. They are comparable in complexity to entire operating systems.
When Google makes a change to the Chromium project everyone follows suit, lest you fork it which leaves development and ensuring interoperability entirely up to you. The complexity of this task depends on how far you want to take your browser.
Even those who fork Chromium will pull changes made by Google to the original Chromium project because making and maintaining your own web browser is really, really difficult.
I quite like GNU