The mental power set is also a Controller role. This means you gain special effects to your powers in controller stance. At level 12, you can purchase Pyrokinesis in the Telekinesis line of powers. This ability locks down your target's healing abilities, which should make Cyborg a lot easier to deal with. If you reach 16, the Psychic Shock power in the Illusion line will perform the same function. The effects do not stack, though, so if you want to save your power points, try to purchase only one.
Other abilities you can use are Terrorize (lv. 8 on Illusion) or Cryokinesis (lv 16 on Telekinesis) to reduce your target's damage output, and Thought Bubble (lv 12 on Telekinesis) or Phantom Flames (Lv 12 on Illusion) to reduce enemy defenses.
You can increase the duration of these effects by raising your Dominance stat. Every 2 points of dominance increases the amount of damage your target can take, before the debuff effect wears off, by one health point. That means the higher you dominance, the fewer times you have to use your debuff abilities and the more straight damage attacks you can do.
Another method for improving your chances are to earn skill points by completing Feats. Weapon lines have nodes which give you bonuses for your stats, so purchasing them will give you permanent improvements regardless of what weapon you equip. Though there are not a lot of feats you can do early on, you can get them for completing collections, investigations, and alerts in the cities, selling any extra collection items on the Broker in the Hall of Doom for spending cash. Races are a good way to earn feat points and style items as well. You can spend in-game cash at vendors in each safe house to by styles that will also net you some Feats. Also, you can get a total of 310 Feat Points (translating to 3 full skill points) just by completing all the exploration feats for Gotham and Metropolis (the Booster Gold explorations are a separate feat from this). These feats can be done without any combat, but I suggest doing them on a PvE phase so you don't have to worry about well-meaning heroes ruining your day. Good luck!