When people say 'required' they do not (generally) mean literally. Being a suboptimal class won't keep you from 100% of the content, but it will keep you from a good fraction of it and make your gaming life much less fun. This atmosphere leads to frustration and people quitting, which is why they don't make MMO's like this anymore. Use all the logic and reasoning you want, the truth is (as has been pointed out many times in the dozens of threads like this one) that this has been tried, repeatedly, and it's a bad idea.

Also let's be honest, the only reason these threads exist is because people want to DPS on WAR and DRK. :P