Or, maybe that it shouldn't come at the same time as the second Action Surge? I mean, a fair bit of 5e class feature progression is prettymuch just shuffling to avoid dead levels, I guess. (And, I suppose that, since cantrips scaling wasn't put on any class progression chart - it's by character level - is why it's OK to get your 4th cantrip die at 17th, the same as 9th level spells.)
Really just table aesthetics, past a certain point.
Weapons don't multiply bonuses, Extra Attacks do. I get that it's just not 'quadratic,'... (not even jokingly "quadratic"), nor even geometric, it's still a linear progression.
Like the hypothetical, not exactly joking, Linear Wizard, above, who only ever gets 2 slots that just get higher level, and only ever swaps out spells for leveling, learning new ones only when his INT mod goes up.
I was saying extra attack multiplies damage. Gaining additional slots doesn't multiply anything out, however. Adding slots lets spell casters use spells more often. Concentration, action economy, and lack of auto-scaling outside of DC's prevents any additive or multiplicative effect. Twin spell does on a limited basis and eldritch blast does because it works like extra attack. That's not all spell casters or spell casting.
Extra attack is just a really good ability. That's all.