Except the idea of diversity also includes individuality and creativity. Things the Borg lack hardcore.
The Borg "Bring Order to Chaos". To them, Individuality is Chaos. Multiple independant voices speaking out but never agreeing on anything. Kinda like typical politicians most of the time.
The Borg do not innovate. They only steal and adapt what is useful. That is how they learn. Not through experimentation, but by assimilation. Taking what is better and making it their own.
Literally what the Borg are... is the opposite of what it means to be Human really. We thrive on our differences. We learn from our mistakes and improve based on our creativity. Some of our greatest achievements... were total accidents! One of the most widespread antibiotics... was discovered by accident!
The Borg have none of that, and do not want any of that. They are basically just machines that will take and take. Anything that is better they take. Anything that is worse they leave or destroy. Hell... they don't even bother assimilating the Kazon for crying out loud!
Biological and Technological distinctiveness does not extend to cultural. All it means is they will take whatever biology and technology that will improve the Collective, and discard the rest as useless waste. No different than taking a log, turning it into lumber, and discarding scraps.
Their obsession with the Federation is because they are the one faction that has so successfully resisted them. So obviously there is something superior within the Federation that can be assimilated and applied to the Collective. The problem with that... is that what is so superior is not biological or technological. It is something that cannot be assimilated. Something that cannot be analysed or quantified. Something that is beyond the comprehension of Hive Mind Assimilators.
Creativity, Courage, and Strength through Diversity.