I normally have the same opinion but if I play D&D I keep my opinion out of the game, because it is too much work to change D&D to my opionion.
Are you talking about the 3.0 or the 3.5 version of heal?
If a cleric casts a heal spell, which is level 6, so the cleric is level 11, he can not attack in the same round.
He can either cast heal or do the same amount of damage to an enemy with a damage spell.
If you reduce the potency of a heal spell then you also have to reduce the potency of the harm spell.
The heal spell has two functions:
- to cure ability damage, blindess, confusion, being dazed or dazzled, deafness, disease, exhaustion, fatigue, being feebleminded, insanity, nausea, sickness, being stunned and poisoned.
- to be a powerful healing spell.
Without the heal spell the maximum hit points a cleric can cure without applying any meta-magic feats is cure serious: 3d8 + max. 15.
At high level the PCs have many hit points and monsters do much damage.
If you change heal you also have to change the damage the monsters of that levels can do.
With a modified heal resistances and DR are better than in a core game.
YMMV: D&D PCs are designed as super-hero and it is a high magic world. If you want a hero who suffers from a mortal wound then you have to play another system, because IMHO it is too much work to change in D&D.