To rely purely on first hand accounts from those who were there would be to completely to ignore the important role of archeology which continues even now to provide us with valuable information that often confirms or calls into question those accounts.
So just for that alone we cannot rely on the memories of those who were there, all of whom had specific agendas be it to protect or reinforce the reputation of themselves or others or to spin events to reflect their personal political viewpoints.
If you don't like the 'spin' of a particular historian, it further reinforces the need to read many historians to get a broader picture and form your own opinion. Sometimes it even provides the information you need to determine the factual truth.
There is nothing wrong with learning from archeology. I was at a gun show, a very high end auction, where they had a saber recovered from Little Big Horn. There have been digs there which have uncovered a trove of bullets, all of the locations marked, the bullets ID, which we are fortunate to have. There may have been one survivor but even if there were he spoke little english and the unit was split so at the end of the say he could reveal little.
When the historian becomes agenda driven, and rewrites history on the basis of what they want it to be, it troubles me.