I don't want to start the game at level 10, but the game campaign itself feels like a higher level campaign.
I really like the idea of vignette's or scenarios that are class specific, mainly because it provides a mechanism to get folks who are not familiar with DnD to understand the basics of their class. That said, I understand it would be quite the undertaking since we know the classes will grow beyond 6. if that is the case you can always break things down through intro scenarios along the lines of melee, arcane, and rogue, or something like that. Personally, I think it's an investment in the growth of the game the more people that try it, having no previous exposure to DnD, and get hooked.
I agree strongly with that and also think the game needs to make more of an effort to introduce itself to people who are new to D&D
There is room in the plot to explain the PCs being somehow level drained back down to zero due to being mind flayed, if that's a thing that people need to suspend their disbelief. But things like having a background vignette could function as a tutorial. I think the way they set up there opening they could definitely handle a class starter before the main game launches.