>>1950606Modulation is absolutely necessary when your brakes are extremely powerful and you don't need ANY effort to lock the wheels. Basically never the case when using road bike brakes from the hoods, the braking angle is so ineffective that I've never had brakes that would have too much stopping power.
With flat bar, v-brakes can be enough to necessiate a need for some modulation, especially with fresh pads, perfect adjustment and good stiff levers. There is a product for this, which is the power modulation noodle, though I have never used it and I've only heard bad things about it. Cantilevers have a smooth modulating lever feel due to the dynamic mechanical advantage, but also require more effort to lock the wheels. Perfect brakes would have indeed an dynamic mechanical advantage but also the effortless lever feel of hydraulics.
>>1950564What kind of adapter you bought? If it's a v-brake to disc brake adapter, pay attention to your frame, it likely can't handle the braking force on the seatstay and ends up cracking. The just get the Maguras for both rims, though I'm sure you can get a new frame for the same price.