Only problem is said publisher needs to know how to do use that leash, and MS has rarely proven me to know how to do that, while time and time again has proven the very oposite.
I'm not sure about that exactly.
Aside from Crackdown and Halo, I would say their other studios have been successful at product delivery, (whether they were intended to be game of the year contenders is another topic) most of them being smaller projects.
Both Crackdown and Halo suffer at the same issues:
Scope.
Crackdown broke down under the pressure to deliver a cloud based solution
Halo broke down trying to make the blam engine do sometihng it's not.
Bungie is also having the same problems scaling Blam, which is why Destiny largely has massive problems with content creation and we see tons of re-use. There are loading areas everywhere, where if you somehow moved too quickly, you'd get hit with an abrupt loading circle. Other times many of their dungeons have entire 'loading' fights where you fight while the ghost is loading the next part of the level.
So I would say it's largely the engine that is holding both teams back from doing great things.
I'd probably go a step further an insist that XGS stop listening to its fans entirely. That's probably the biggest lesson they should learn from Sony Game Studios. GG pitched a game where you fight robot dinosaurs with a bow and arrow, the fanbase would have lost their shit and forced them into killzone 3. But now HZD is an established and loved IP. The same goes with God of War changing its style to away from what it was. And if ND asked fans what they wanted for TLOU2, it would have been more Joel and Ellie going around busting up people, and not the game they got today.
We can go on and on about how fans aren't really the best barometer to follow when developing a new title. They are good for feedback after a title is released, particularly around MP game balancing, but definitely should have no say in a future work in progress.