People try to find meaning everywhere. The idea that there is a rigging on the matchmaking that isn't disclosed by Blizzard is a conspiracy theory, that would include a good bunch of insiders in the company who would have the knowledge that such algorithm is in place. There has been no such leeks or indications. Such algorithm would have little benefits compared to the backlash that would ensue if it was discovered. There are many arguments against this idea, but as always with conspiracy theories such as this one, a debate feels like a waste of time. If you disclose any evidence (statistical data on a large sample, or indications in the matchmaking code), that could indeed grow into an interesting story, but I doubt that will happen.
First, it s highly unlikely that "a good bunch of insiders" at Blizzard would have intimate knowledge regarding precisely how their matchmaking algorithm for a game like HS works. This sort of thing is quite technical and knowledge pertaining to the actual state/inner working of such algorithms is likely restricted to a very small group of coders that maintain/develop said algorithms. Second, these individuals have almost certainly signed NDAs, which would make any release of information pertaining to their work illegal (i.e. they would lose their jobs and face legal action if they released information). This is common industry practice. Of course, concrete evidence for something like what we have been discussing would be virtually impossible to come by seeing as no one on this forum has direct access to the matchmaking algo for HS and thus would not be able to uncover "indications in the matchmaking code". Nor is the sort of manipulation that we have been discussing something that would show up in statistical data unless values were skewed to extremes and the system were only matching up brand new players to 11x gamers, which obviously is not happening. So I suppose you could assert that matchmaking manipulation is a theory, but certainly not one that could be disproven on the grounds that you cited in this response.