The fact that your warlock (or any other) levels give you 9th-level casting slots does not have any relevance to what spells you can prepare. It's only relevant in that your cure wounds spell can be cast with that 9th-level slot you got from your warlock class to heal 9d8.
I agree with your intent. I just want to clarify that Warlocks don't receive spell slots higher than 5th level. All spell-like abilities that Warlocks have at 6th through 9th spell level are gained via Mystic Arcana
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At 11th level, your patron bestows upon you a magical
secret called an arcanum. Choose one 6th-level spell
from the warlock spell list as this arcanum.
You can cast your arcanum spell once without
expending a spell slot. You must finish a long rest before
you can do so again.
At higher levels, you gain more warlock spells of your
choice that can be cast in this way: one 7th-level spell
at 13th level, one 8th-level spell at 15th level, and one
9th-level spell at 17th level. You regain all uses of your
Mystic Arcanum when you finish a long rest.