Maltrax was as overpowered as you think.
He had a specific amount of control over all heat, including body temperature. He could increase the heat of just about anything organic or inorganic. So far, the only source he couldn't master was the sun. But he knew why, the sun was protected by Azarath.
He could create amounts of fire if he so chose, but the bursts were always short-lived which made them difficult to do battle with. Fortunately as his own body temperature rises the easier it is to transform the residual heat into flame and eventually scorch his opponents. But should he lose control of his ability it would mean the end of him. Whether he preferred it or not, he was human.
He had at first assembled a team of allies to defeat the Justice League. However after the Thanagarian invasion he lost interest in justice and turned to evil. He reorganized his Alliance of Truth into the Alliance of Fire, creating simple ranks to demonstrate his supremacy above the others. His daughter was the one he worried about. She hadn't displayed signs of any remarkable powers...yet. But he did fear that if she did, she'd rise far above him and kill him.
There was only a few tokens he needed at this stage in his plans. He needed to be able to absorb a large amount of excess heat continuously and carefully to protect his human body. Once the human body adjusted to the temperature he would attempt to absorb a nuclear weapon without detonation. Should he fail he might die. But he may be able to absorb enough of it to keep him from death... but this was unlikely. So he had to be well prepared.
He also needed the boy... Time Zone. A hero unknown to the Justice League or the Teen Titans. The teenager master of time space, and the Guardian of Trigon's newest prison.
...
He opened his eyes.
Another nightmare.
Joshua rolled over in his bed, it had been a long night. He had been forced to battle a Titan's willpower and mind to suppress the access to Azarath. Not easy.
He spent the majority of the previous day circling the planet, trying to fix some of the time pollutants and alter the mismatches left by a long since forgotten battle.
He also visited Gotham.
He witnessed firsthand the Batman step out of the shadows, scowling at his old partner. He even followed the Caped Crusader and Batgirl into the BatCave, stealthily avoiding any detection.
"That was weird. Why was Dick in Gotham?" Batgirl had asked.
"He suspected that I had a hand in JLU intervention in an attack on Jump City. He came to investigate."
"How was he dumb enough to trip the alarm? Is he that out of touch?"
"His girlfriend is Starfire of the Teen Titans. She came from another world as a prisoner and crashed here. He developed romantic feelings for her and lost sight of the mission. She tripped the alarm, not him"
Batman turned back to his computer.
"Don't even think about it." Batman scowled.
But Batgirl was all ready gone.
So was the BatPod.
Batman simply could have deactivated the motorcycle, but he chose not too. It was high time he started working alone again. Maybe the Titans would take her in.
Josh stood from his bed and rubbed his eyes.
A flash of light appeared in front of him.
"Never a dull moment, Time Zone."
"You know it." Josh said, walking to his closet.
"What have you discovered?" The being behind him asked.
"Maltrax is planning to use my power to make his body strong enough to repel the power of Helios. Then he'll absorb Helios and use its limitless power to destroy Azarath, the place not the man."
"And?"
"He plans to attack me and free Trigon of his prison. On the second strike is the one where Trigon will handle the Titans at that point Maltrax will attempt to kill me in combat. While the other members of the Alliance of Fire attempts to defeat the Justice League." Josh explained, pulling his black suit over his torso and his pants under him. He clipped them together with his laser sword he stole from Chucko the clown when he was cast into the age of the dinosaurs. He purposely ripped it in half and hid the other half behind his belt and under his black cape. The § stretched to perfection on his chest... § the symbol he wore resembled the Teen Titans and the Justice League on either end, not touching directly. The circle was the thing that connected the 2... their commitment to peace and justice.
"Will you be able to handle his attack?"
"Joshua can't." He said, pulling on his gloves.
"What about Time Zone?"
Joshua lifted the mask over his head and pulled it on.
"Time Zone is a guardian... not a warrior. There is only one enemy I have ever been unable to defeat. Alas, Maltrax can not possibly imagine my nemesis and will not. Time Zone will defeat Maltrax. Then Maltrax will stop attacking Time Zone."
"Why?"
"Time Zone is practically invulnerable aside from his adversary mentioned previously." Time Zone said, speaking in 3rd person to demonstrate that he was 2 people. Time Zone AND Joshua. He removed his mask. "Joshua isn't even close."
He put his mask back on and completed the clock circle with his right arm, time to move backward.
He clipped his mask onto his cape and onto his back.
"Where are you going?" The other being asked.
"Its never where... it's always when."