Lars Levenwood:
I believe when it comes to base damage, ammo costs and overcoming DR energy weapons are already superior. Reducing resistances vs those still further could be unbalancing.
That said my comment assumes D&D 3.5 is balanced. Cue the laugh track.
Oh there are things that need to be heavily tweaked with 3.5, but yes it is balanced; and by balanced I mean each side has equal access to the ridiculous levels of power.
The problem that I see people have with balance is unfortunately there are so many rules listed in so many places that no one person knows/follows them all.
3.5 is not a rules light system, and when people treat it as rules light a character becomes able to do a thing that should not be possible. that exploitation of ignored rules then creates the case for why the rule they are ignoring should exist. The "lack of a rule" is then seen by many as a fault in the system for not having a rule to protect against the thing for which a rule already exists.
now within the rules there is exploits,...
...like how you can sometimes deal 5-10x the "falling damage" you take, ...as "falling object damage" to someone or something, just because of weight and fall speed of an object.
...or...how the crafting system can allow 3 gold pieces to be crafted with 1 gold piece worth of raw materiel (no special feats, literally ALL PHB reference materiel) and it can be done by a lvl 1 commoner who put 1 skill point in (craft-general).
but yes I do believe the immunity should be changed to a resistance.
(energy) immunity should become ...
(energy) resistance {10xCR}...per round