My solution would be to increase hp-pools while keeping healoutput constant and to spread incoming damage more.
Right now we have fights that are basicly raidbuster - 10sec later tankbuster -10 sec later raidbuster - 10sec later tankbuster....
And in fights like this hots and gcd-heals are ineffectiv because you HAVE to heal all dmg instantly or a dps will die from a prey or some other mechanic.
That is why SCH ogcd are that strong: you have many and you dont need more.

having bigger hp-pools would make hot stronger while limiting mitigation, it should also make more room for new healermechanics like combo-point-healer or dps healer,
because you need your hard hitting aoe heal ready the second the raidbuster happens and having your combo not ready at that time could cause a wipe.

what my mainproblem is: you dont ask for a better designed class - you ask to be more like SCH or AST.
you want more mitigation, effectivly beiing more like a SCH and therefore be a petless SCH
you ask for more raidbuffs, making you more an AST

but i NEVER read here: "please make WHM a stronger hothealer to give us more opportunitys to dps"
you dont ask for WHM to be a WHM, just a healer with different colored spells.

and that is just not what class-design is about.
and that is why SE will probably never give you what you ask them for.