One thing to consider is that the cloak is less flexible than the AC. There are a lot of ways that you can reliably impose disadvantage which become useless when using the cloak.
For example:
- Lying prone
- Taking the Dodge action
- Using Patient Defense
- Hiding
In all of these situations, the AC is strictly better.
A class that often finds themselves forcing attackers to have disadvantage may find the clockcloak to be essentially useless, and the AC to be far superior.