The only discriminators were Storm Shadow and RAPTOR, and there is a compelling argument to suggest that those are key.
I don’t think that there is any truth to the lack of upgrade potential - indeed at Cap EA the Harrier was Saturn capable and had a path to a MIDS capability.
For a time the jet could carry 6 x PW4 plus Sniper whereas the Tornado could carry fewer - I think because the SMS had an issue born out of its original KRET functionality.
At the end of the day though it matters not!!