What we can say for sure is that fully justified paragraph stands in tradition with typography in general. Most books and academic papers from the past were typeset in this formatting style. While using a flush left formatting is a bit unusual. The interesting situation is that all three examples need 11 lines to show the content. That means even activated hyphenation won't safe space that much.
A second fact is that thanks to the LaTeX internal algorithm the example with the justified text looks very good. That means, the white spaces between the words are not visible and the text looks well formatted. Nevertheless the difference between flush left text and justified text is small. It is mostly a question of personal preference. And most texts in the internet and on smartphone displays are formatted in the flush left mode except pdf documents which are mostly formatted in justified style.
The perhaps most intersesting question is if flush left paragraph formatting is something which has to be fixed. Or let me ask it different. Is there a need for firefox and other browsers to display text justified or is the existing flush left rendering future ready? The situation for screen layout is the opposite as for printed layout. Screen formatting was from the beginning working with the flush left mode only. It is ver
In theory the CSS Specification has the ability to render a text in justified mode, but nobody is using this preference.