There’s very little grinding in the overworld, if any at all. The grind comes from the dungeons, in which you want to rush to max difficulty as soon as possible.
Lowering the world level is a severe hindrance to your progression. The mobs become easier, which is very bad for you if you want to learn how to play Spiral Abyss correctly. Sure if you whale you never have to deal with the mechanics, but short of spending thousands of USD on the game you will have to learn to deal with the mob mechanics sooner or later.
It is better for you to learn it in the overworld rather than trying to do the same in the Abyss.
The only benefit to lowering the world level is to allow you to play with your friends, who may not be at the same level as you are. There is zero benefit for the grind.