As @clarkiestooth says, the stiffness of the boot has a lot to do with whether a player will feel undersupported (I think this is what people mean by sloppy when they’re talking about stiffness), adequately supported or restricted (oversupported). Different strokes for different players, though, literally. The stride length, as a function of the player’s natural body frame, of say Grabner versus Toews will have a large influence on where these over and undersupported lines get individually drawn. In my personal experience, a significantly overlooked component in this equation is tongue stiffness. If there’s room to go down in tongue stiffness, a stiffer boot can still allow for adequate forward flex.