That's rubbish. Slowing down doesn't improve the ride, just prolongs your time in the turbulence.... the test pilots have it right. Turbulence penetration speed is for a category of turbulence that occurs very very rarely.
As far as I have read, nearly all the major severe turbulence occurrences have occurred in clear air With little, or no, prior turbulence to slow down for. But nearly everyone slows down at first bump, for no other reason than they see everyone else do it. Sheep operating procedure!