That Salesforce created it was wrong. That Heroku was already that way, yes also re-painting history. Cedar and buildpacks were conceived before the acquisition but launched after. The teams were allowed to continue executing on roadmaps for multiple years after the acquisition, but Salesforce could be viewed more like a series b, c, d round than in a way influencing the roadmap and making it happen.
GitHub is an amazing parallel, folks feel that Microsoft turned around GitHub, but actions and much of the GitHub turn around happened long before the acquisition. Those sort of things take years, you should mostly try to judge a top down influence 4-6 years after they were there.