I agree. If adding additional effects to underpowered heroes could be problematic than it would still be possible to tweak their mana speed and/or damage% to let effects kicks in faster.
For example, a Khagan could need a faster special for sure and/or changing his defense buff to a more offensive effect as a defense reduction on hitted targets.
He is the unsuccessful cousin of Magni and Sir Lancelot and defensive buffs without a heal isn’t so meaningful on a slow special: you would have to hope for another hero to make you team recover.
Another example could be our beloved Elkanen: the game had seen many strong red heroes that are meant to kill green heroes, quickly and safely. Removing every green tank but Yunan from high leveled teams. A simple buff it could turn Elkanen into something useful could be the following:
every HP exceeding the caster’s maximum amount would be redirected to the whole team in equal number, making him a reasonable flanking hero and healer.
I don’t know your opinions but I hope that Vivica wouldn’t still be the only legendary healer available from TC20 when 2019 will come to an end.