Hello, I'm new to this forum and thought I would start with a (not-so) controversial thread.
I personally feel that Scipio "Africanus" is a viable candidate for this topic. I mean, what exactly did he ever do? As far as I can see, all he did was win a few easy victories in Spain and Africa over third-rate generals and armies. Here's a brief analysis of his career:
New Carthage- A brazen and reckless assault that succeeded primarily due to luck rather than brilliance.
Baecula- A complete failure by all accounts that could have cost Rome the war.
Ilipa- A stalemate that achieved no material results.
Utica- A cowardly and treacherous sneak attack.
Great Plains- The Punic army here consisted primarily of levies, who were no match for Scipio's veteran legionnaires.
Zama- Despite every possible advantage, Scipio nearly lost the battle. When Massinissa's horse returned to the field, Scipio's troops were in the process of being crushed by Hannibal's far inferior, but much better led, levies.
And yet, Scipio is undeservedly regarded as one of Rome's greatest generals even though he contributed little to Rome's victory in the Second Punic War. Other, better men like Marcellus, Nero and Fabius deserve far more credit. Scipio was in reality little more than a competent general who was built up by the Scipionic propaganda machine which tried to downplay the achievements of the aforementioned commanders.
So, to conclude, the formula for Scipio's success was as follows:
Veteran, highly trained legions + A general of average ability + Weak opponents = A successful, but unremarkable commander