I was completely under the impression that longbows required strength of 13! Maybe they (and rapiers) should, but I was wrong about this one.
If rapier and bow should require a 13 str... then shouldn't longswords and warhammers require a 13 dex?
honestly, i have yet to see how d8 for rapier (non-light so no TWF) vs d6 for shortsword (light so TWF allowed) is somehow a problem causing actual serious issues in play (vs ones in perception or belief) - and if so what they are.
rapier vs SSD (Shortsword, scimitar, dagger)
Rapier - if you want to use a shield, want a hand free for casting or need bonus actions for other stuff.
SSD - if you want TWF or dont have martials and want to throw the dagger as an option.
basically - whatever the actual play problems are bewteen dex and strength - it aint the rapier at fault.