Not to mention we are completely off topic now. So perhaps we can either make a whole new thread about this to continue or just drop it and get back to the topic at hand?
Horribly off-topic! Fun, but off topic. I'm not claiming I'm totally right either, just expressing my doubts.
Anyway, yeah. The gladius actually has a lot of siblings among late European weapons, but none of them were ever anybody's first choice. Maybe a shortsword is just not that great without a scutum, and I'm not personally sure why the scutum went out of use (like did the longer swords make the scutum obsolete or did oval shields obsolete the gladius? Who knows).
Unlike the gladius, the scutum was never really reinvented. The pavise is sort of like a scutum but was never used offensively. Kite shields and round shields could be convex but were never as large. It's a big question to which I have no answer.