Tweak idea monster enchantments

Danacm

What do you think about a tweak that use the adnd 2 dm guide rule for natural attack enchantments depends on HD ?

"DMG, page 75, wrote:
CREATURES STRUCK ONLY BY MAGIC WEAPONS
Despite special defenses which protect certain creatures from attacks by non-magical weapons, these monsters can be effectively hit by attackers as follows:
Code:
Defender Is Attacker Must Have The Following
Hit By Weapon Hit Only By OR Hit Dice Of *
+ 1 or better + 1 or better 4 + 1 or more
+ 2 or better + 2 or better 6 + 2 or more
+ 3 or better + 3 or better 8 + 3 or more
+ 4 or better + 4 or better 10 + 4 or more

*This does not apply to characters of any sort.
This provides for magical properties and sizes of the attacking monster. Thus, massive hill giants can effectively attack most creatures, and all other types of giants can affect everything save a few gods."

Its a huge improvement for some summoned creatures, elementals etc, but official rule.

Danacm

I found that the shapeshift/shapechange forms nearly use this form about enchantments, but not always. The elementals are 10+level in the game files and uses +4 enchantment, the iron golem too. The greater werewolf is 8 levels, but only has +2 enchantment level weapon. The greater wolfwere is 10+hd but uses +1 weapon only, idk why.
The wolf and bear shapeshift forms has a +1 enchantmentm its just more than needed.