4 more 2nd level spells per encounter, IMO, much better than one 4th level slot. Scorching ray is only 2d6 less damage than Fireball, and a sorcerer can (literally) burn down any boss in a few turns with it.
Scorching ray is single target, fireball is AoE.
And the higher the level get, the more you will miss high level spells.
And besides, neither fireball nor scorching ray are all that effective.
Where sorcerers really shine is twinning haste, so that your GWM fighter and Paladin both double their damage output
