Sorry for putting this in a kind of pastebin (couldn't fit in character limit), but I hope my thoughts help progress this discussion;
There's plenty you could say about the applicability of concepts between matchmaking and serious gameplay but the biggest issue that continues to go unaddressed broadly speaking, although you somewhat worked towards addressing it yourself, is that matchmaking in its form exists at all.
The fact that players are automatically placed into matches with random strangers in this specific format is just going to lead to poor gameplay. The solution is that players must be organized in a more human way, with in-client PUGS, and like you touched on briefly, is an actual ladder/tournament system, where the PUGS function not only as a place for players to improve their skills, but to onboard people towards the more serious ladder system. Players LOVE playing LFG 6v6's, why not make organized team play an integral part of the "ranked" system in Overwatch?
The existence of a "queue" in such a system is, in my opinion, wrongly assumed. It's just but one way that matches could be organized for such a ladder/tournament system and it's usually assumed when gameplay is only arranged by algorithms and not by actual human staff, and primarily because it's far easier (read: cheaper) to try to automate things than actually organize them with people.
I know you'd like to personally tip toe around this kind of criticism, given your employment, but the way I view it is that Blizzard doesn't/wouldn't be interested in investing the human resources into developing such a system. Any such system would likely be entirely volunteer based (and imo entirely unethical if ran by a company like Blizzard).