One thing that annoys me in all D&D editions about the Wizard is the ability to learn ANY spell. (And yes, even the 5e Wish spell can heal better than a Cleric can!)
This derives from old school, when the Wizard (namely Magic-User) was THE spellcaster. It covered any spellcasting concept, from sorcerer to enchanter to witch. So it could cast any spell.
In new school, the spellcaster has evolved and radiated into different kinds of spellcasters: Bard, Druid, Psion, Artificer, Sorcerer, Warlock, etcetera.
The entire D&D spell list divides up into about
thirteen different spell themes.
I wish the Wizard would have a narrower focus and be more specialized in which kinds of magic the Wizard specializes in. I want this thematic focus for the sake of flavor. But it can also reduce the extreme versatility of the Wizard.
Suppose.
At level 1, the Wizard must choose only two out of these thirteen spell themes. Some might want Necromancy and Fire spells, some might want Enchantment and Force spells.
At each higher tier, the Wizard can select one more theme: at levels 5, 9, 13, and 17. By level 17 that totals six themes, almost half the spell themes in D&D. But not all of them. Perhaps the Wizard only gains new themes at level 9 and 17, totaling only four themes by the Legend tier.
When gaining new spells at each level, the Wizard can only gain spells from one of these known themes. These are the themes that the Wizard has affinity with − a knack for.
If the DM wants, the DM can allow the Wizard to find and figure out how to use other spells that are beyond the known themes. But the DM has control over which spells the Wizard can find. Meanwhile, the gain of spells while leveling still keep up the thematic flavor.