Mythic is an easier way of saying "content above level 40". So Mythic Levels are the addition of levelling from level 40 to 50. In some ways Yes, in others No. The stat progression is as close to Epic level progression as possible, but there are some limitations. The engine doesn't allow players to be over level 40, but your character file will be changed to include all the stats that you would have. Various scripts have also been changed to think you are over level 40. So your character sheet will still say you are level 40, but the game will behave very closely to you being high level.