I look at it this way- the cost of victory is resources saved. The value of every action is in how many resources it ultimately saves the party from spending.
If you can kill enemies faster, you use up less resources (such as hit points). But if killing enemies faster consumes a valuable resource (like fireball), then it's value isn't in how much damage it did, but how many hit points it saved your party from losing.
If the merit of a spell slot is how many hit points it prevented you from losing, then it becomes easy to see that healing spells are simply broken from a design standpoint. Using the example of an enemy with multiattack (I'll pick a brown bear for this), we have two attacks for 8 damage and one for 11.
Slowing the Bear makes it easier to kill and reduces it's average damage to 11 from 27. Paralyzing the Bear, even for 1 turn, protects you from 27 damage (and making it even easier to kill!).
Yet a level 3 Cure Wounds, even used by a Life Cleric with 18 Wisdom, only prevents 22.5 damage for 1 round. It requires you to be in melee range of the enemy, putting yourself in harm's way.
I don't see how anyone can say that better healing spells would be broken, or "require" healing classes, when they are so inefficient compared with other methods of preventing resource loss to a party- but as I said above, that ship has sailed, attacked by pirates, and lost at sea, lol.
The problem is also two fold. Other methods of preventing damage are better than healing, yes, but healing insid e combat also is useless when you want to retain your damage output.
Characters are as efficient at 100% HP as if they were at 1% of their HP.
But because healing is usually less than the damage a creature makes, it also makes no sense to waste a healing spell on somebody with 1% HP to get him up to 8%, because the next attack will do 10% damage, bringing him to 0 anyway.
So the only useful use of healing in Combat is to bring a character back from 0 HP.
We could bring back the bloody condition or be even more gradual, like:
Bloddy: When you are below 50% HP you have disadvantage on ability checks.
Very Bloddy: When you are below 40% HP, your speed is halved.
Extremley Bloddy: When you are below 30% you have disadvantage on attack rolls and saving throws.
Ultra Bloddy: When you are below 20% you only can take an action or bonus action or reaction per turn.
ULTRA EXTREM BLODDY: When you are below 10% your speed is reduced to 0.
Now it makes sense to heal, because we have several thresholds of worsening conditions.
At the moment the only threshold for any effect is 0 HP.
Of course with such conditions the chance of a death spiral gets higher.