When I reached Level 140, I still needed to grind my character because I need to reach Job Level 70 before I can go above 140. A friend recommended that I level up in Wasteland because the Exp points are decent. He also suggested that I do the main quest in order to get a damage boost buff while inside the Wasteland Map.
I don't usually do Main Quests but this is an exemption.
Get Damage / Experience Boost While Grinding in Wasteland
1. Do the Main Story Quest.
I'm not sure if this is the first one, but look for the the quest similar to this.
2. As you progress to the quest, you will encounter the Divine Tree. 3. Soon or later, you will unlock the Divine Tree which will give you several types of boosts depending on what you need.
4. I immediately maxed out the Surging Strength I then followed by Rapid Growth 1
5. You can check the Attribute Overview for all your buff. Here's what mine looks like.
6. Here's some quick testing before and after I upgraded my Divine Tree buff.
Before. ~159k Crit vs Wildness Piranha Plant
After. ~250k+ Crit vs Wild Piranha Plant
The materials you need to unlock Divine Tree Buff can be acquired while doing quests and grinding in Wasteland.
Hope this helps.