I never thought O’Reilly himself was unfair to Trump. Not really sure why anyone else would think so either, unless they’re grossly misperceiving the situation.
As far as other individual hosts, I thought Hannity was very fair, as well as Greta.
Fox News in general was often a different story though, and there were a few lengthy stretches of time where they were basically running wall-to-wall negative coverage of Trump. Hence part of the reason CNN of all things began to be considered as offering more fair coverage of the GOP primaries.
I don’t find however someone or a station critical at times and favorable at others bad. In fact I prefer this. I then get to see all sides and not just the side through a lens of what some prefer to be unicorns and rainbows. Some challenging and critical as unfair no matter what is stated or reported ( not implying you here). To that I say grab a tissue because it hasn’t even begun and we should be thanking those that have been critical to prepare the cantidate. Because ugly hasn’t even started yet.