It’s the least worrisome because it can be abolished (selectively)
I’d say it’s because they don’t command the police or military and are completely subject, without input, to the democratic levers of government including, not least, amending the constitution itself.
They sit completely under the constitution, and it itself is a democratic entity. If the amendment process doesn’t feel democratic enough, well then we get the elephant in the room about how much democracy do you want and whether that’s maybe your main problem.
If cooperation is not at least partially optional, then it’s not the weakest branch
What other branch is partially optional?
In the case of a court, they’re role is passive. They only act when prompted by a party who brings a case. Legislators and the Executive do what they want when they want. So surely they’re by the most optional. Honestly have no idea what you’re trying to say here … the point of governmental power and law is arguably not to be optional.