@Hadski wrong answer, I can tell you something right now without making spoilers since I saw the raw of all the chapters left until now.
He is not an OP, you have also seen the screen of his statistics in the first two chapters and they have nothing abnormal, the reason why everyone treats him as garbage is because he is a healer and healers behave like parasites since in this world nobody makes strategies where this class can be used to the best.
The protagonist having played a lot of video games means strategies, so he knows that there are spells that can strengthen allies and weaken enemies, he knows various strategies in practice.
These are basic things that are not calculated in this world, here they think only of brute force, wasting lives (the first to die are healers) and precious time, making the battles last much longer than they should.
In all honesty I don't know if anyone in that world changes their mind, in the chapters the protagonist spends more time in the dungeons at the end so not much is known but it's surprising to see how the members of his party react to the basic support spells, stuff to ask you how that world has not yet died out.