After he was weakened due to Kryptonite. Superman was called upon specifically by Cyborg to pull the motherboxes apart as he's got planetary strength for example. And the plan was for Superman to fight Darkseid as an equal, who is almost certainly not nukeable either.
Of course. Superman is obviously way stronger than Barry.
Can you cite this? I find it hard to believe he'd be doing an IMP considering Flash was seriously hurt by a parademon laser here.
A quick Google search would show you exactly what Zack said. What does Flash being hurt by a laser have to do with his ability to punch at the speed of light? He literally ran at MFTL speeds when he time travelled, and considering what Zack said, punching at SOL is a no-brainer for him.
You are absolutely right about Flash being the most powerful as someone who literally has reality under his thumb is pretty much unkillable. But hopping timelines to kill someone as a baby isn't the same as beating them down in a fight, which Flash hasn't shown the potential to do here to Superman.
Yes, he is the most powerful. Although considering that he could just punch at the speed of light, that's enough to kill Superman.