Let's be very clear about this subject. You have to separate the man, James Comey, from the office he held as Director of the FBI.
Comey probably deserved to be fired. If there was a guy at his level better at putting his foot in his mouth I can't recall him off the top of my head.
The problem is in firing Comey with immediately filling the void of the Russian interference investigation with say a special prosecutor, Trump impinged the integrity of the office of Director of the FBI.
When you are playing with this sort of explosive stuff you not only have to be right you have to have all of the appearance of being right.
Trump is pretty good at putting his foot in his mouth as well. It's seems clear that he has lousy advisers.