It can actually work. Because, if someone is serious about where they want to spend their money, i assume they are going to do a bit of looking around for reviews. And eventually one will have a good idea about which developer puts out what quality content. But this doesnt penalize the legit developers and their users for purchasing from the marketplace by delayed updates.
This model have been working in other marketplaces as well like orbx, aerosoft, just flight simmarket etc. You just gotta do your research before spending the money.
And i don’t think Microsoft actually QA tests the aircraft as the developers intended. For example in a plane with deep systems simulation, the dev will probably have a lot of tests they do before releasing. What Microsoft probably does is check if the add-on works on a basic level or not. Microsoft probably doesn’t test if a particular system is simulated properly or not. This is a speculation ofcourse. And if with current testing, products like captain sim c130 can make it to the marketplace, then you can imagine the level of testing that goes on.
Edit: Aircraft is just an example, i meant to say any addon.