Consider that not everybody you don't like is a "failure." By their own lights, they may have succeeded. Carter surely not, but the other two did manage to stay in office and win high approval ratings.
How would you factor in that many Presidents did not have "Executive" experience before becoming POTUS and actually did a good job?
Tricky question. Most of them had been governors, generals, or heads of government departments -- all executive positions. The three who went directly from the Senate to the White House -- Harding, Kennedy, Obama -- certainly weren't the best bunch.
Garfield and Pierce also weren't great. Pierce was downright awful. Maybe Truman and Lincoln, neither of whom had been governors, did alright. It's not an easy question to answer. They succeeded I guess, but made a lot of mistakes along the way (bear in mind though, that the judge's position Truman had before the Senate is supposed to have been an executive, rather than a judicial position).