Ahahaha! Fighting the final boss of Abyss for like the third time, and this time, I went and defeated it with a POW HAMMER of all things. One of the weakest 'spells', and that's the 'final attack'. xD
Exactly, fusion weapons are awesome, but they don't stand up well against higher difficulty levels, while they're great for Muliplayer. Plus being able to customize the weapon's abilities, and to a degree, how it works gives a sense of pride as you beat on other people and their own prized weapons.