"Thank you so much. I appreciate that you took the time to find this and reply to me."
Happy to help. This stuff gets super-complicated quickly. My understanding, and this comes mainly from passing conversations with other lawyers, is that it's a grey area.
If they expressed a waiver clearly and expressly, as it appears here, they may have a good case that you have no inspection rights.
There is also the question of whether you have to expressly consent or not, or if, after the fact, they handed you something that said "oh, by the way, congrats on waiving your rights"
FWIW, although I am not a lawyer, I do not read that the same way you do, to say that the waiver is unenforceable. Rather, it says that the corporation cannot unilaterally take away the right of inspection. That does not mean you cannot give up the right in exchange for something. In fact it strongly implies that you can as long as the waiver is "clearly and affirmatively expressed."
'Clearly and affirmatively expressed' meaning in terse legalese, 6 point font, on page 16, section 2, sub section iii of document #8 of your HR welcome package.
TL;DR A stockholder's right to inspect under Section 220 ~may only~ might only be able to be removed via statute.
EDIT: Edited to reflect IANAL and the statute might be up for interpretation.