Because starting with R8/9/10 classes that deal +1000% damage make things easy right?
You already can buy buffs that increase your damage absurdly high, making the game even more boring since you are playing Saitama mode.
Dungeons feel like a walk in the park till you get to 230, even so, you might be able to solo it if you are on a cleric tree build.
We already have an easy mode game, you want it more easy?
Now to make it a good suggestion, they could make the all classes unlocked 1 rank earlier (except the R2 classes and hidden ones) to increase the variety of builds.