A note about attack and defense roll variance :
In Master of Magic, each "sword" is a roll with a base 30% chance to do 1 damage, and each shield a roll with 30% chance to negate one physical damage
(With some units/magic items increasing the 30% chance, each "+1 to unit" increasing this chance by a flat 10%)
This means that an unit with 10 attack versus one with 3 defence will on average do 3 damage, with one negated by the defense roll.
This both reduce extreme rolls (a dragon even with 30 swords will almost never do 30 damage, but it will be almost assured to do at least 5-10 against most opponents)
For what I understand, in Elemental, each roll is a linear chance between 0/1 and your attack/defence value, so a unit with a defense of 50 has as much chance to roll a 1 than a 50 or any value between, and the same is true with the attack roll.
Merit/Advantage: it prevent high defense units to be immune to low attack ones
Flaw/disadvantage: very high variance/random impact, making even high level units/heroes killeable with a bad defense roll or two and making tactical combat more random.
I prefer the MoM version, as with the default 30% chance a unit with 3 swords can still damage sometimes another with 10 shields, it's only with extreme values that the system seams to break (a hero with 20+ def. is more or less immune from most normal units attacks, except for illusion attacks (phantom varriors), armor-piercing or negating attack, high attack units and creature such as other heroes, dragons, etc ...)
Note that it is hard to have a hero with such high defense (and almost impossible with some heroes chassis like some spellcasters), and the game limit you to 6 heroes, you will probably only have one or two like that, and it will already be near the end of the game. Moreover, one invicible hero can still be killed with the appropriate spells (or by dispelling some of his defense spells making him much less invicible), and a hero cannot be everywhere at once, so armies are still usefull to defend your cities or raze the cities.
But I'm not opposed to the elemental system, provided that at least something be done to the current squad rules.