There's another point to be made regarding player experience.
Since without full share, you are usually punished with an agonizing and inevitable defeat when your teammate dies, sometimes through no fault of your own, player deaths are often followed by toxic interactions between teammates, "moron" tags peppered around the map and stuff like that. Full share helps a lot with this problem.
It also seems to me that people more often stay in the game instead of leaving immediately when full share is on, maybe partly because they want to see their stuff put to use. For one thing, this means defeat feels less bitter since fewer rage quit. But it also increases the chance that dead high rated players instruct lower rated players on their team, and that dead low rated players stick around to learn from their teammates. These are the only times casual players get to see high level play and actually pay attention to it, since very few of them spectate games or watch replays, and actually incentivizes high rated players to teach, since they can salvage their rating if they guide their teammates to victory.
These are not minor concerns. This community is plagued by the unreasonable popularity of maps like astro craters or thermo or gap. If a lobby features some other map, it's almost always rating limited. New players end up joining the only lobbies that will have them, the aforementioned shit map trifecta. Some never leave this comfort zone even after gaining a white rating.
TMM is one of the few developments in years that has a chance to change this, and, if I'm not mistaken, it's whole purpose is specifically remedying this situation. We should not overlook player experience when deciding how to structure team play. Even if it turns out full share is not the best option, TMM should arguably use it at launch to be more noob friendly.