Theodrin and Faolain offered their oath of fealty freely, so they don't count.

Nisao, Myrelle and the circle were offered by Egwene to overlook what they had done and keep her silence about their misdeeds (which at the time was politically dangerous to Egwene if the Hall found out) if in return they swore fealty so she could know they were loyal and not trying to usurp her authority and scheming in her back. They were supposed to be loyal, especially Sheriam as Keeper, but the women did what they wished and saw the Amyrlin as their personal puppet. They mistepped, Egwene/Siuan found out and took the opportunity. It's manipulative, but not tyranical. Egwene merely gained a bit of the ground she was supposed to have as Amyrlin. She left the women no choice but to see her as the Amyrlin.

What Egwene asked of the circle was no more than what rulers expect of their advisors and nobles. It gave Egwene political power as Amyrlin over the women only - the power an Amyrlin should have but Egwene didn't, but not absolute power. It was up to every woman who swore to decide when what Egwene asked fell under her authority and she went beyond these boundaries (they refused to tell her who the AH were notably - and she could not compel them to reveal it). Under Tower Law, Aes Sedai are already supposed to obey the orders of the Amyrlin, if they are lawful.

This is quite different from the fourth Oath Elaida had in mind, of complete obedience to herself, more or less the same oath the BA hunters used, which is essentially compulsion. All the AS could do would have been what Elaida didn't expressely forbid and what the three oaths don't stop. All she ordered they would have been bound to obey, however crazy, however unlawful, however disastrous. What Elaida had in mind would have destroyed the system of checks and balances of the Tower.