There is no guarantee that the range of values in which a mechanic will be balanced, and the range for which a spell will be fun to use are going to have more than an tempty intersection. Sure, for most mechanics it's going to work out fine (and I think it should for out fine for balance), but it would be nice if people actually are aware that tuning is far from being easy, and whence check wether a mechanic can be tuned within a reasonable range. Otherwise we'll only end up with neccesarily untertuned mechanics post tuning phase.