You get 3 methods to recharge your level 6 slot,
Pearlescent amulet, Illithid Freecast, and the same thing on a staff.

You can cast Twinned Chain Lightning 2 turns in a row, and use lower level spell slots to recharge your sorcery points.

But oh no, somehow having more spells slots or higher spells would be broken!

As people pointed out, calling level 7-9 spells too powerful while handing us all these illithid powers must be a joke.