This is a concept long standing even back in Jesus time. What a parable is? A parable is the making use of simple concepts to illustrate a less obvious point. To the Jews immortal soul, hell, lake of fire, eternal torment etc. are Jewish concepts back then. Both Pharisees and Essenes held these concepts. So are the Jews in majority as they are influenced basically by the Pharisees.
From Josephus,
In this region there is a certain place set apart, as a lake of unquenchable fire, whereinto we suppose no one hath hitherto been cast; but it is prepared for a day afore-determined by God, in which one righteous sentence shall deservedly be passed upon all men; when the unjust, and those that have been disobedient to God, and have given honor to such idols as have been the vain operations of the hands of men as to God himself, shall be adjudged to this everlasting punishment, as having been the causes of defilement; while the just shall obtain an incorruptible and never-fading kingdom. These are now indeed confined in Hades, but not in the same place wherein the unjust are confined.
If there's a problem in the concept, Jesus should have corrected it instead of making parable out of them.
You have the same problem as with Matthew 25:46, "Everlasting Punishment" does not necessarily mean "Everlasting Conscious Torment". Since the punishment is a result of being thrown into a lake of fire, the everlasting punishment could as easily be being burnt to ash in the lake of fire. Josephus didn't say in the passage you quoted whether he thought the everlasting punishment consists of everlasting torment by the fire in the lake or everlasting destruction by the fire in the lake. As usual, those who believe in eternal conscious torment read their doctrine INTO the words "Everlasting Punishment".