to use Diablo 3 as an example, recently i was playing through the xbox version, soloing with a wizard, and playing on the Master II difficulty, which i think is MP7, but anyway, after getting through ACT 2 or 3 on NG+ pretty handily i then faced Zoltan Kulle, and whatever the archdemon is you have to fight just after, both of which could one-shot me, which turned the fights into a farce of rolling around between attacks, which was never guaranteed to keep me in the clear no-matter how careful i was. the only other solution was to go and re-organize my gear and build to give myself more way more health. what i did was just drop the difficulty, because i was pretty sure my original build would work just fine on Master II once i got into the next act, and yep, it did.
if i can reach that part of the game with my current build no problem, and carry on after those boss fights with the very same build, again no problem, what is the point in putting that wall up in between the two? to force me to rebuild for bosses? to force me to co-op? i don't get it.