i can explain!
Look, currently the only class that could even use this engraving would be support.
So let’s get to the points
1 - Currently the support encores are: Awakening, class, expert, drops of ether, vital point and in the six slot (if you have ancient acessories) you run heavy armor 1 or 2 (in bard or artist) and judgment or heavy armor in paladin.
Wath vital point?
To get a basic idea, no stagger in the game is designed for the need for bombs. Yea! It’s not supposed to be necessary, however, in order not to be necessary, all classes need to have their entire stagger rotation. That is, nobody has. So in a larger stagger, it is necessary to use bomb.
But to illustrate better, when you use vital point on a bard, you can give up some tripod or some high stagger skill, and put something more useful or even just have more stagger and give up using bomb just to have another bomb for personal use (dark grenade) for example.
2 I saw a comment saying “but you can take more dark support grenade” Indeed you can! However, each dark grenade lasts about 20 seconds, and it only takes 1 person to throw it. If 4 people take dark grenade, that means we have 4 minutes of dark grenade. That’s enough for almost every fight, and any more would just be despair or waste.
In summary: explosive expert is useless, although there may be someone who will say that it is useful, we still don’t have a NEED to use it. Just like, nowadays, supports don’t need heavy armor before reaching 6 engravings (but it can be used).