The demon generals had forgotten about the fact that they didn't just have to end the fight quickly, but also prevent him from getting close to the SD (Shatter Devourer).
They never thought that it would be this hard to suppress Alex, even with all of them together.
Yes, they weren't using their true powers, but look at the stats!
Alex was supposed to be Legendary 3, yet he was fighting Mythical 3, and now he was even forcing them to use their real power.
How could they've known that they were fighting with someone who had been a protagonist in the last world?
Alex would never be transported to an area that could get him in a disadvantageous situation, not until his starting point was a world in which he had been a protagonist.
Luck might never increase more than EX-rank as that was the highest luck one could have, but luck should never be underestimated.