Wish->simulacrum needs fixed. Though that applies to all casters.
They could use a generalist sub-class. One that focuses on the classic "get all the spells" mentality, with some features that let you utilize them a bit better.
i.e.
2: You learn 2 new level 1 wizard spells, and increase the number of spells you learn when leveling up to 3. In addition, you have twice your proficiency bonus for arcana checks.
6: As a bonus action, you can rapidly prepare 1 spell from your spellbook. Once you do this, you can not do it again until you take a short or long rest, after which the spell is no longer prepared.
10: You can copy ritual spells of other classes into your spellbook, but only cast them as rituals.
14: As a bonus action, you can rapidly prepare 1 spell from any class spell list of 5th level or lower. Once you do this, you can not do it again until you take a short or long rest, after which the spell is no longer prepared.