We don’t know if a lower monk casts heal spell more often than a max monk (it could be true but maybe for example for very few decimals of difference and wouldn’t notice visibly that though) but from what i see it has always the same Heal Rate from lvl 1 to lvl 5.
Also if you have a max troop is always better than 2-3 levels less like in this case of the monk have 200-300 healing effectfrom a lvl 3, is always welcome (it makes you save for example in a bad situation those 200-300 more).
Obviously its boost Mad Monk is something totally different:
- Faster Heal Rate
- More healing received
- more damage
in practice you have something really meaningful to use especially with Black Magic. And especially with Mad Monk that you really see the difference when it heals the towers, they regain those 5000+ health again which makes the base tougher to beat moreover if there are also frenzy frost blasters making you waste precious time or your most powrful spell.