I was using a bit of hyperbole to make a point. I'm going to focus entirely on AST for now but most of it applies to sch too. As long as AST can buff the party and heal the content there's going to be no reason to pick a whm who can't do a part of that. Even if you reduce the most ironically named card(balance) AST is still just a whm with buffs and out of balance. Hence remove all their buffs.
Of course there are other interesting ways you could balance this. Whms traditionally have been able to inflict moderate damage in FF games. In FF1, while no damage dealer a whm's hammer shouldn't be under estimated. They've always had holy, in ff9 for example Eiko was easily on par with vivi for damage dealing once she got holy(i'm ignoring summers cause well, that's a summoner thing). So given that you could of course neft AST heals to the point that they seriously struggle to heal and have to spend most of the fight not DPSing. Whm on the other hand has large heals which afford them time to do a lot of dpsing. The balance comes then from AST cards, the whm does direct damage and the AST makes up for their lack of personal dps through indirect damage(party buffs).
The point is balance should be achieved by looking at overall party contribution, not just HPS. Increased HPS is of not real value if it's not improving party contribution.