This very question has asked quite a bit...
BG3 makes use of the DnD 5e rule set and once you past level 12 some of the spells become over powered and would be very difficult to implement. This is a limitation of doing a CRPG as there is no live DM to make judgement calls that would help balance these spells. As such going to higher levels create a scenario where they either have to lock down a lot of spells or develop the single most sophisticated AI in the history of computer gaming.
Also as with traditional ARPG design the game has a specific end point, the developers worked around this at level 12 based on the issues mentioned with the 5e rule set.
I understand your argument DYNIA that this is a CRPG and not DnD Table Top. However the CRPG has been always designed to be based on the Table Top experience and so make use of a variant of those rules and thus must work within those limitations.
Exactly the level 9 spell Wish is OP even by Table Top, if the DM aloows it you could use wish to become a God if you want it, however other things the spell can do without DM intervention is
Cast any 8th level spells or lower without any requirements like components,
Create a non magic item that no larger than 300 ft in any direction that values to 25,000 GP,
Allow 20 creatures you can see to regain all hitpoints and remove any status effects,
Grant up to 10 creatures resistance to a damage type you can choose,
Grant up to 10 creatures you can see immunity to a single spell or other magical effects up to 8 hours,
You can undo a single recent event by forcing a reroll, (Basically Save Scumming).
Most of these option while OP are still pretty lame compared to what the DM could allow this Spell to do.
