I think it has to do with the higher level of training the channelers in the Age of Legends had. Now I do allow that certain groups, such as the Windfinders and the Wise Ones, have certain specialties that none of the Forsaken can match, but overall, the channelers from the prior Age are very powerful, and we've only seen Lanfear and heard of Semirhage performing mass destruction. There were mentions in TOM that any Aes Sedai could quickly destroy a dozen soldiers - I believe Galad said this.

This is probably why the War of Power was so destructive, and I think it mainly came down to a matter of the Aes Sedai or the Forsaken trying to neutralize each others weaving so their forces could hold an area. RJ hinted at this when he talked about Gateways and the strategic implications for a battlefield.