Pretty sure it's not because they were revived recently. MC just wrecked the stuffing out of one of the Demon King's Generals who wasn't there during the final battle a few chapters ago. And they're both supposed to be the most powerful beings of each race. The only issue MC got with his powers was that he could no longer use the energy humans used for their magic, but MC has already replaced that energy with the energy demons use. They mention in this chapter that humans naturally aren't as powerful as demons due to racial differences (the Hero/MC being a different matter). It's weird if you think about how it seems MC and co. are the ones having trouble here.
Bruh what is with this horrible power balancing? These are early enemies and MC and co. are top tier characters. Theres no reason MC shouldn be able to curbstomp them.