> The reason Windows doesn't have fragmentation is because it's a closed-source operating system with internet enabled functionality that is centrally controlled by Microsoft with an iron fist.

Sure, being closed-source prevents fragmentation from the start coz there's nothing to fork from, but it's not a requisite. There are many open source projects with less degree of fragmentation with major marketshare winners that the ecosystem can target for, and you can mostly recommend people to use without too much thinking, e.g. browsers and web servers.