Earlier quoted context omitted.
I disagree that a high vit + end build is bulletproof. I'm absolutely certain that most anybody could destroy that build easily in PvP. One of the great things about the build system in Dark Souls is a build that is great for PvE may not be a great build for PvP.
Okay, so it's bulletproof for PvE.
Basically, the question is how many times you can hit the boss by taking advantage of their timing versus how many times you screw up trying to take advantage of their timing.
If you have more HP you can screw up a few more times but if you're not dealing much damage you end up having to avoid screw ups for a long time in some boss fights.
Then there are the fights like the Four Kings where you really want to be doing higher DPS or else things get really messy.
Personally, I found the easiest build for PvE to be a sorcery build focused on high DPS. With a high enough intelligence you can deal a lot of ranged damage, which makes avoiding being hit that much easier.