There are two types of duties:

"Leveling" duties, which include any duties in the following level ranges: 1-49, 51-59, 61-69, 71-79, 81-89, 91-99

"Max Level" duties aka "High-level", which include any duties at these levels: 50, 60, 70, 80, 90, 100

Leveling duties have always been designed to give lots of experience points, while max level ones don't give any until they are modified to do so after the level cap increase. The max level ones usually are not scaled to give much experience.

So, from their perspective, it's an oversight. However, in practice, it doesn't matter and nobody really cares about the distinction. So it's odd that they have seen that as a priority over almost any other pressing issue in the game.