The Oaths aren't completely effective, because AS aren't entirely trusted, but without them the White Tower would be be a world-ruling dictatorship rather than just a powerful faction which pulled strings to prevent wars for 3000 years.

Not to mention channellers already outlive normal people by a factor of 4-5. They could become virtual gods if left unchecked.

It's a classic case of who watches the watchmen, and the Oaths are part of resolving that. They aren't enough on their own, but in Randland they are necessary because there's no system of Ji'e'toh to ensure honor or da'covale to ensure obedience.

Egwene's fault isn't that she commits monstrous acts - it's that she tries to control things too much. This can have dire consequences but so far there haven't been any that stand up to close scrutiny.