> it covers time, but not adoption.
And you can't really cover "time" in an objective way before first determining some reasonable threshold for adoption, which is about as hard to objectively define as it gets. This means all the data presented in this article is basically meaningless.
For example, _way_ before Github we already had open source code hosting & collaboration servers. Trac comes to mind, but there's an even better example -- Gitorious, which also came before Github. Why did the author not even consider these two examples and only named Gitlab es the "replacement" for Github ? I could understand the omission of Trac since perhaps it was not primarily Git-based, but Gitorious? Gitorious was even at one point the #1 Git platform, eventually surpassed in popularity by Github (and much, much later by Gitlab).
Is this a "proprietary alternative replacing a open source one" ? How do you even take this into account in your "Time until OSS alternative" metric ? It just shows how meaningless this all is without a subjective definition of "alternative" or "replacement". There is no way to present this objectively as the authors are trying to do. The entire data set is manipulated to fit their point.
The rest of "replacements" are similarly questionable or even ridiculous, because, depending on your definition, they either ignore alternatives that came much earlier (because surprisingly frequently a proprietary "service" replaces a popular open source program) or call a service "an alternative" when it is simply not.