WHM is not doing that badly, in fact the healer comp I would want is WHM/AST instead of AST/AST or AST/SCH. Why? Because WHM does the highest damage for a healer. Now imagine them with the Balance buff on them. Then they do massive damage (for a healer) making WHM utility come in through their damage output, healing output, and ability to save people from mistakes.

The problem healer right now, the one that needs the most help, is SCH. Nerfing AST wont help SCH when people would still bring AST over SCH unless you nerfed AST to the point they are basically do not offer anything of value. So just buff SCH up to be consistently comparable in value to the others.

Also the only way to truly make AST OP would be to give them the ability to draw the card they want every time. Where if I hit draw I pull all 6 cards and can choose which cards I want to spread and royal road.