In my opinion, the main problem this book has had has been that it is dry, which is to say lacking in Eros and Thanatos and the relatable emotional impact that brings.
A book staring Stark should, in my opinion, be basically a blend of Doctor Who and Sherlock. Doctor Who blends the power-fantasy of a scientific super-genius with the relatable angst of grieving for lost loved ones and the many people he failed to save. Sherlock has the power-fantasy of being a super-genius blended with a weirdo's struggle to protect the few people capable of loving him.
A book staring Riri should, in my opinion, be basically a blend of Doctor Who and Buffy. A scientific super-genius who mourns the many people she's failed to save, while dealing with teenage issues like her first boyfriend or girlfriend, and how her general weirdness makes getting one of those problematic.
I do believe that either character could work if that is how they were written. Power fantasy, eros, and thanatos in properly engineered combination creating an effective entertainment product.
Instead, both characters have largely lacked that proper engineering. They tried to make Stark this really dry story of a politician/businessman responsible for all of the world's large-scale boring political problems. And they made Riri so fluffy that her book makes "Moana" look like "The Seventh Seal".
Both equally dry, just for different reasons. I've seen nothing that suggests that this will change. Dryness is the problem, not melanin content or plumbing. Changing melanin content and plumbing didn't fix the book last time, and switching melanin content and plumbing back won't fix it now.