If some of these are answered later don’t spoiler as I haven’t read the comics
Why did they want to conquer Earth but not the Thraxans? Omniman says they’re gonna kill everyone on the planet
So Mark has been getting destroyed because he’s holding back and the moment he stops he’s able to take out that female Viltrumite. But when he was greeting wrecked by Omniman or Battle Beast he was still holding back? All it took was for mark to try to kill that lady and she got destroyed, instantly.
Nolan’s pretty strong, but there are various viltrumites that outscale him, it’s even said in the comic that the reason they have a chance of winning it’s because they won’t be sending their most powerful soldiers.
Also, the way the scene is set up makes pretty clear had Mark not hesitated he would’ve won