We hear that diseases of the mind were very difficult to heal but the implication was that talent Restorers could do. However, the taint causes a madness that is just one of the symptoms of being inflicted with it, with the others being bodily decomposition, loss of physical control and loss of cognitive functions (i.e. some tainted male channelers become braindead or regress to incompetence rather than or before going insane) - since the taint didn't exist in the Age of Legends until very late (and even then it took a couple of years for all of the male Aes Sedai to notice it), it seems to me that the Restorers of that time didn't have a cure or treatment for the taint, but at the height of their society they did know ways to treat mental illness.

With all that being said, I definitely see your point about how Healing the taint while saidin was still afflicted would just be a temporary solution - especially given how random it could be; some male channelers never went insane or decomposed while others went insane very quickly.