I have to disagree with your hypothesis here. You make some interesting and compelling points, but you don't have to look any further than FFXI for a counter example of "needing slightly larger weapons to stand out". The
Joyeuse was incredibly understated, but was the envy of virtually every RDM and quite a few PLDs. More importantly, the players became quite skilled at identifying high-tier weapons like this (Ok ok, I know Joyeuse hasn't been high-tier in years, but that's beside the point) by sight very quickly. Personally, I felt very... shiny... every time I put on my RDM AF and strapped on my Joyeuse.
Big
can be an effective way to indicate "awesomeness", but it is quite possible to make understated weapons that look unique and desirable. That being said, don't get me wrong, I think having a wide variety is probably a good thing. SE did seem to dry up for ideas in FFXI and I would hate to see that happen here, especially this early in development.