What has been refuted? That the Medieval Warming Period and Little Ice Age didn't exist? That Mann refuses to allow independent verification of his code and data? That others using similarly discredited techniques to Mann produced similar results? That the Bristlecone Pines proxy reconstruction failed to correlate with modern temperatures? That real temperature data was spliced into these reconstruction graphs to hide this issue? That although advised not to, he used the Tiljander lakebed sediments in another reconstruction. And not only did he use those lakebed sediments, he used them incorrectly?

I think one needs to be a little more specific.

Just because someone is well educate doesn't absolve them from being wrong. Resplandy et. al. 2018 is a perfect example of this.