The conclusion would only seem biased to me if I thought they were biased in their procedures and analysis.If I am not mistaken and remember correctly both "Inside The Target Car" and "The Ruby Connection" seemed to conclude that The Warren Commission came to the correct conclusion. So it does seem biased.
I could be mistaken.
If their processes were scientific and as accurate and objective as can be, the conclusion is what it is, not that it is conclusive.
Either side could claim bias if the conclusion was not the one they wish to believe but it doesn't mean it is true.
Even a completely impartial, non-biased, competent, and objective documentary would be sure to piss off one side or the other.