I did that and didn't have any problems connecting by 6" flexible duct work with a 6.5" Hose Clamp.

The uncrimped side of the solid duct pipe is significantly larger than the vent opening, so I feel like increasing the crimps and managing to squeeze it in would leave it under some tension.

Any decent range hood, if not your local building code, is going to require solid duct pipe with smooth walls.

I tried for an hour, in the attic, to compress or expand the solid duct pipe to fit inside or outside the vent opening...until the adjustable elbow I was using broke.

Replaced a restrictive duct vent.

The 6" duct opening should be at least 2"-3" for easier installation of vent duct and a anti-slip raised rim at the bottom

The crimped end of the solid duct pipe is the exact same diameter as the opening on this vent.