Yes, exactly. The material in the lead just summarizes, in one brief sentence, the later paragraph on Boswell's material. That is what the lead is supposed to do.
On the blog, first, it does not mention Sergius and Bacchus, the subject of this article. It's just a general criticism of Boswell's ideas; the mere fact that an image of the saints appear on the cover of his book is immaterial. Moreover, it's a self-published blog and not acceptable as a source here. Time to move on.
Your current addition of the Harvey is also redundant, as we already say that "Boswell's methodology and conclusions have been disputed by many historians" and include six citations for it. Ironically, you are only adding more weight to this particular part of the article. t/c