Overmelded gear is supposed to be a luxury. Any buff to melding chance (even if its 5%, which is a lot to a 11% meld) will only lower the price of the associated materia since people will need less of them, and also the final value of the item.

Take the two most commonly melded sets:
i) Slaying acc (with vit)
- A quad-vit meld gives you a piece of accessory which is arguably superior to the 210 drops if you need the extra vit. @1.5mil-2mil a piece for "top of the line" equipment can be considered a bargain.

ii) Crafting gear
- You can always just ask someone to craft the 2star pieces for you. Those who have invested in the overmelds... well, it's an investment. Currently, by investing millions into 2 star equip, crafters gamble the investment can be justified in the future with the release with 3 star crafts. Those who don't craft as often should just pay those who have the gear if they don't want to invest into the gear themselves.