Hey MC, maybe you should... I don't know... stop them?
I know it's going to work out in the end because it's this manga, but this MC keeps on letting the bad guys finish casting the, "Kill everyone" spell after loudly proclaiming that they're going to cast a spell that's going to kill everyone.
To be fair, they went from pulling out the device to activating it without missing a beat and it's not like he knows how the device works, so it makes sense to gather information before taking any action.
It's also somewhat consistent with his personality, and sometimes it works in his favour, sometimes not. For instance, when the evil dude came to get samples of the cursed flowers, he delayed putting a barrier around the slimes, and getting detected, because he analysed right up to the last moment if the evil dude could actually see the slime and was targeting it. That worked in his favour and he was able to follow the evil dude back to their lair undetected.
He just always waits until the last moment to take a decision. And while it might not be a practical trait, it certainly is an entertaining trait since we get to see him deal with ridiculous threats that he just let develop.
And also, the villains in this manga are comically evil. I'd personally be as shocked as he always is at finding an endless number of mad, genocidal magic scientists organisations that keep creating ridiculous weapons of mass destruction. Meanwhile there's essentially no one showing that level of genius who is not genocidal, so he's just soloing absolutely every evil organisation around. XD