The problem with some "historians" is that they allow their political and social bias to influence their version of history. One of the worst offenders was Nancy Isenberg's biography of Aaron Burr. She found excuses for durn near every bad thing he ever did. That's hagiography cloaked as history. I find Burns is guilty of that from time to time, and he has publicly admitted he has a political and social agenda in his work in the past. Doris Kearns Goodwin, a two time plagiarist who paid bundles of money to those she stole from to avoid prosecution, mixes her political beliefs with her history in spots, too, though she's not as egregious as Burns.
A worthwhile biography presents all sides and lets the reader decide. You've never seen David McCullough, Hans Holzer, Robert Caro, or Walter Issacson shade their history writings.