It's always annoying when people complain about a chapter while seemingly ignoring every chapter proceeding it. MC's magic is just unique magic, not a win button. He can't revive the dead, he can't insta-kill powerful monsters, he can't stop people from being stupid, and if he is careless with how he uses it the magic will backlash at him.
For example, if he tried to use the word(s) for "Die" or "Kill" and it backlashed he would probably die, if he tried to use a two or three word spell and it backlashed he would probably die, it's not that complicated.
Don't forget that his more powerful spells are the ones with more words, and those take more magic power and time to use, so even if he wanted to use them, and he's been trying to avoid using 3-word spells if he can, he would need time, and the bears rushing at the big bad bird monster, would give him like 3 seconds which he couldn't have managed at this point.