I really would prefer if people would tell other people "to level up" if they encouter a problem. As in many cases, leveling up or getting better gear is not the solution to the problem. The problem here is - as stated by many others - that you need to interupt the one shot mechanic.

Stop telling people to level up or gear up, if you can teach them the proper mechanic. This man learnt what an interupt is. And because of this he will clear many different bosses that will come along his way. Interupt is a base mechanic that needs to be learnt.

If he does not learn it, he will have problems in the future. If he learns to level up and gear up, he will end like the people claiming that Spirit of Vengeance is too hard in story mode and needs three nerfs to complete it. Teach people mechanics. Not "level up", "gear up".