Many of their darkfriend enemies will not be readily identifiable as darkfriends, and the oath will stop them from fighting them unless they are 100% sure they are darkfriends (which may not ever happen, and will waste valuable time even if it does.) The oath also prevents them from fighting in battle unless they feel as though they are in danger (thus allowing them to use the OP "to defend their own life".) That basically eliminates any possibility of using any type of strategy; e.g. they can't stand at the top of the Tower and lob fireballs at the enemy because they're not "close enough" to the danger to bypass the oaths.

Half the reason the AS sucked so bad at fighting the Seanchan at the Tower is because they were prevented by the oaths from doing half of what they could have done. The only person who put up a fight was Egwene, who of course was not bound. Not to mention that many of the Aes Sedai's enemies, such as the Seanchan, may not be darkfriends at all, but are still an impediment to victory at the LB and must be dealt with.

All that is just the third oath. The second oath (don't make any weapons for one man to kill another), is nearly as bad. If they could make weapons, they could multiply the good guys' strength many times over just by making Power cannons (as a random example) and leaving them with each army, or Power-tipped crossbow bolts for the Legion, or whatever else. Even just some more Power-wrought swords would be useful. But they can't do any of that.

And about the first oath, the less said the better. AS have made a science and an art out of tying the first oath in such fine knots that it all but doesn't exist anymore. At this point, it's more of a mockery than anything else. There's no benefit at all to taking the oaths. It's not like they make regular people trust them more; if anything the opposite is true. I don't see why any Ashaman would take the oaths, and if the AS have any sense they'll get rid of them posthaste.