Extra Invocation as Feat for Warlock?

[bid]

Reductio ad absurdum would require you to find a similar case with similar ambiguity where the ability breaks down if it is allowed to scale with character level rather than class level.

Allowing character levels for warlock invocations implies that you allow 9th spells to anyone who gained a 9th slot from MC.

I'm sorry. I thought I was clear enough the other 2 times.