Because I’ve read the description of the data disk, rather than blindly applying it because it was purple and only has 1 dot.
The disk tells us Enemy units cannot be defeated whilst the leader is still alive, but can be instantly defeated. That’s exactly what happens when you equip the disk.
You may have interpreted this as meaning the leader can be defeated by normal means, but that wasn’t my interpretation. The enemy leader is an enemy, so is subject to the same defeat conditions as everyone else.
This disk has uses - it will help players who need to complete feats that require applying debuffs multiple times without exhausting lots of energy doing so because enemy teams are defeated too quickly. You, and others, seem to think that any and all disks that come as rewards from completing feats should automatically be helpful if people just apply them without reading what they do. This isn’t the first disk that can negatively affect your team, and it likely won’t be the last, which is why it’s important to read what they do before applying them.
As for the question about relic level and character level, I don’t see how that’s relevant in this situation.