What are some reasonable "average average" numbers for mundane damage? That would give us a ballpark for how much lower blasting damage needs to be.
I was about to ask the same question.
Let's see. Assume a generic dude with greatsword at level 10 (the level Fireball stops scaling). He's probably got 22 Str (18 + 2 race + 2 enhancement), and the cleric hit him with a Greater Magic Weapon so he has a +2 sword. Optimization by the Numbers says the average AC for a CR 10 is about 23, so he should optimally power attack for about 2. Total average damage per round comes to something like 28, more if he can get some more pluses somewhere.
Weapon Focus, Greater WF and Weapon Specialization if a Fighter. That gives potential for additional 6 damage.
Rage if a Barbarian. That would be also 6 more damage. 8 if we give the Barb WF.
Smite if a Paladin. At least 10 more damage, more if he has decent Cha. Also depends on spell choice.
Two-handing (6 + 3 = 9) a +2 greatsword (2d6 => 7 + 2 = 9) and Power Attacking (2). With two attacks that makes it 40 average damage in a round. And that's just baseline, with no real optimization. Heck, I should add some obvious feats or class features, because using those is barely optimization, but whatever, it's not needed.
A 10th level Fireball will deal 35 damage on average. That's less, yes, but in an area, so it can actually be much more. Also, it's just an average, so it can be even more than that.
With my houserule the d6 would turn into a d4. Average damage would then be 25. A much more reasonable number, IMO. And the maximum damage would be only equal to the non-caster's damage.
(It's my first time "analyzing" mechanics, so if I did any errors, tell me.)
If someone optimizes for blasting then that's okay with me. Optimized blasting is not the problem. Banning or limiting metamagic misses the point and screws over non-blasters.
If AoE spells are a major problem, you could increase the damage (or leave the damage as is, if you really want to nerf them), but split it among all creatures in the area.
They're not.
Damage is the problem. You have an interesting idea, but it does nothing to non-AoE spells. And they still can be used against a single enemy.
Guys. If you post an idea, please explain how it's better than my houserule. My system mastery is too low for me to figure that myself.