We don't need much, just a couple of small, focused changes is enough to spice things up. For example, for the damage side of things, all I would ask for WHM is to reduce Dia's duration to 12s (because 30s feels stupid), and to add a new Water/Banish GCD with a 15s CD. That's all. That's not going to suddenly make WHM gigabrain to play, you could even make a macro to auto-use Banish if it's ready and Glare if it isn't, if you wanted.
As mentioned elsewhere, you never saw these 'healing is boring' complaints back in Stormblood when AST had it's old cards and SCH had it's DOTs. All we heard back then was 'can we make WHM as fun as SCH/AST and not have these trash Lily thingys', and SE heard that and went 'ok, we have reduced the fun of SCH/AST to achieve fun parity, enjoy' instead of just doing the SHB Lily fix to SB WHM and building on it from there
'More healing required' would be a more 'thematic to the role' solution. It'd also absolutely devastate the more casual players and likely cause an even bigger exodus from the role than we've seen. Abyssos ramped healing required, and we're in the situation we're in now. It got so bad that even JP started asking about the shortage