I'd say that the problem is most obvious with Enchantment specialists, since they by necessity run into it as early as 4th level: there is only one 2nd level enchantment spell in the PHB (Tasha's Hideous Laughter). A 10th level abjurer would run into the same problem (Dismissal), as would a 12th level necromancer (Circle of Death), 14th level enchanter (Insanity), 16th level diviner or illusionist (Discern Location, Screen), or 18th level diviner, enchanter or illusionist (Foresight, Dominate Monster and Weird).
It's a bit odd that one of the mid-tier schools, Enchantment, has three levels of spells where there's only one spell of that school. Then again, many of the Enchantment spells are quite powerful (Sleep, Hold Person, Charm/Dominate stuff), so perhaps it balances out.