Spartacus? Maybe. Perhaps he was an exceptionally good fighter.

Most Gladiators? I find this unlikely.

First of all, a real Roman soldier fought as effectively as possible. A gladiator was also fighting for his life, but his equipment was designed to make the fight entertaining, not necessarily to optimize effectiveness. For example, a murmillo, in spite of having an elaborate helmet and arm guard, had no torso armor, because leaving a spot open that an enemy could stab was presumably more entertaining to the crowd than having fully armored gladiators. The retiarius, equipped with a trident and net, was also equipped in a manner that was, as far as I know, non-existent among real soldiers.

Roman legions fought in ordered formations, presenting a wall of shields with swords and spears sticking out. Many of their enemies -- with some exceptions, such as the Parthians -- generally fought in similar orderly heavy infantry formations (although differing in details: e.g., a Macedonian-style pike phalanx and a Roman legion were both tightly ordered, disciplined infantry formations, but very different in detail). Battles between tightly formed infantry formations could be slow, grinding, indecisive affairs, such as five hours of fairly indecisive action in the Battle of Ilerda: i.e., not very entertaining.

In short, a Roman lanista wanted crowd-pleasers. A Roman general wanted war-winners.

A gladiator might usually be able to beat a Roman legionary if the Roman soldier had been equipped as a gladiator and put into an arena fight, though: i.e., circumstances much more similar to the gladiator's typical experience than the legionary's.