This has been debated into the ground. And you won't find any absolute truths with regard to disc brakes, except the fact that they stop better in the wet. Maybe you should try a search?
Disc brakes are not commonly found on road bikes because they are not commonly needed or desired. They add expense, complexity, and weight. They are also banned from UCI racing events.
My opinion - if you plan to ride often in gravel and the rain, then disc brakes are a good idea. There is a small weight penalty and your bike may ride a bit rougher due to the stiffer fork, but this will probably be a worthwhile trade-off for you.