I just want to point out that if you go back and look at older editions, spell damage hasn't really changed much, but hit points totally have. Case in point, the humble Fireball. In AD&D, it did 1d6/caster level. Monsters had d8 Hit Dice and rarely added any bonus to this number. Players had at max 10 Hit Dice of varying sizes and other than Warriors (who only got 9), the maximum bonus was +2 per die.
2nd Edition capped fireball damage at 10d6 at 10th level.
3rd Edition was exactly the same as 2nd, but now players got up to 20 Hit Dice, and larger monsters had grossly inflated Constitution scores. I mean, just to compare, a 2e Ogre had 4+1 Hit Dice, for an average hit point total of 19. The 3e Ogre had 10 more hit points.
Now in 5th edition, a Fireball does 8 dice of damage. And that's that. (Yes you can upcast it, but at that point, it's no longer a 3rd level spell). And oh hey, an Ogre? FIFTY NINE hit points. And his CR is 2 instead of the 3e Ogre's CR of 3.
So don't tell me that they couldn't have increased damage to compensate.