Exactly.
The D&D Wizard has the power of Gandalf or (Malory's) Merlin, the versatility of Dumbledore or (Disney's) Merlin, and the frequency of Doctor Fate or (DC Comics) Merlin. That is, phenomenal cosmic power (up to and including literally rewriting reality), the ability to perform almost any act one might want to if you just have enough time to research the appropriate spell, and a power supply that is theoretically limited but practically inexhaustible because it's always at least somewhat under the Wizard's control.
Every other D&D spellcaster has limits on at least one (and usually multiple) of these things. The Sorcerer emphatically lacks the versatility, doesn't quite match the power, and (especially if you want to use spell points much) some of the frequency. The Cleric, Druid, and Bard all emphatically lack the versatility, a bit of the frequency, and the top-end power (unless, like the Bard, they borrow the Wizard's power.) And all other spellcasters simply cannot reach the frequency and power of the D&D Wizard.
And yet, even though those other classes all lose out on at least one part of the Wizard's potency, some of them aren't especially great for balance either. Bard is IMO the closest to being actually balanced, having a limited spell list that it must selectively choose from and substantial non-spellcasting resources that play a major role in the class doing its job. Druid is probably the closest to the Wizard, in that the Land ones can replicate almost all of what the Wizard does, and their spell list, while not topping out quite where the Wizard's does, is still extremely versatile and reaches some pretty high heights.