I disagree, sorry. I think the system is really well tuned. A 14% chance, well it's not great but on that item you've already overmelded twice which brings the % lower for each consecutive try and well, 14% it's not bad either.
Sure, it sucks to be screwed over trying to meld a simple materia and failing everytime, believe me I know! This happened to me yesterday, failing 11+ times on a 24% chance! wtf?! But that's the design and it works, it gives the game economy lets noobies make a little extra gil converting their items as they level up and makes things like penta-melding with level 3/4 materias that have 2-9% chances or whatever it is, bloody incredible if you get lucky enough.