I don’t think either that such a wing would stall at 6.5 degrees of AoA, but I would rather think that a level flight at such AoA/attitude is unsustainable due to the lack of available thrust versus the tremendous increase in drag in a low air density environment.
Any change in stall AoA from ground level would be almost entirely due to Mach effects, not the altitude density. The low drag cruise bucket would be at quite a high Cl
Perhaps you should be thinking and talking in terms of Cl rather than AoA, because that's what really matters