For the Wizard (not to be confused with the Ranger animal companion that should not be called a Familiar), I really would prefer :
- one free cast per day to represent Ritual casting ;
- make them more similar to 5e (they do no damage as such), though the various effects per type is cool in BG3 ;
- unless destroyed, the Wizard can (5e) make the Familiar disappear and reappear using an Action.

- Additionally (not a priority) : It would be cool to if each Familiar was considered, by enemies, a normal animal (non hostile) when in a proper environment, until the Familiar does a hostile action. For example, a bird in the underdark would appear red/hostile as they are not normal animals in that environment.

( nb: the Familiar's levelling seems like an oversight / error. )