There was an old maxim about characters as they progressed. Linear fighters, quadratic wizards. Wizard spells increased in power at all levels while fighters just got flat power increases. Keeping spells flat in power unless upcast and reducing their spell slot progression was the way to make sure wizards weren't just better than fighters at everything while keeping general power more measured at the top end of the curve.
Hmmm I'm not sure that the (limited) scaling of leveled spells significantly counts toward the "quadratic" power progression. I'd say that mostly comes from the obtaining of new & more powerful spells, an increased number of spell slots per day, and the various metamagics. Would 5e wizards actually see an
appreciable increase in power if all their 1st level spells did an additional die of damage at levels 5, 11, and 17? If they got another scorching ray at, idk, maybe level 7 or 11?
We also return to the main issue that, in 5e, cantrips are
not "kept flat in power unless upcast". Eventually they even become better than 1st level spell slots, which is nonsensical. Why is something that doesn't cost a resource and is so simple to be "cast almost by rote" more powerful than something that takes a resource?
