I help people all the time.
...people on my own server, who I plan/hope to play with again in the future. Random duty finder cross-server guy #8764764 doesn't matter to me at all.
As for wasting time, of course games are meant to waste time, but that doesn't mean that it isn't rude to turn something that takes 15 minutes into something that takes an hour because you choose to be selfishly ignorant of fight mechanics. Especially when it would take you 5 minutes to watch a video/read a breakdown of the fight.
By virtue of being a hobby/entertainment, video games are (should be) the lowest on the priority list for most people, which means they have limited time in which to do things. If I have an hour to do CT + wait in queue, and get stuck in a group with someone who refuses to understand mechanics beforehand and keeps causing wipes, it is perfectly within my right to be upset that 1 selfish individual is making my goal for the hour undoable.