^ That would be like saying the F-22 Raptor's engines/control surfaces are capable of performing maneuvers up to 90Gs. That's all well and good, but the AIRFRAME can't take that kind of strain and it would fly apart under that force. Whatever the engine's maximum output in theory, there are practical reasons why it can never be put into practice. It's the same story with the Alphas never managing to exceed about 40 knots.
Something like that. A more refined comparison might be like saying a factory-fresh F-15 airframe could do Mach 2.5 clean and 9G maneuvers but a heavily fatigued and constantly patched together F-15 airframe might only be able to do Mach 2.2 and 8G maneuvers. The engines could still push it to Mach 2.5 but at greater risk to the airframe...
While the F-22 can't even supercruise with external pylons attached.
That's actually sort of what I had in mind with "Warp 9.975" being an intentional fudge. Anyone who flies in an Intrepid knows those specs are pretty optimistic, but they quote them anyway because the walls have ears.