I'm not really sure anyone actually understands what this app is. It's some kind of textbased app where you choose a class, press "run dungeon" and end up with sort of loot you can use ..or can't you use the loot...or?
What people usually do wrong is to ignore damage reduction and just stack damage, make sure you're using a few defensive items and skills in your build. There's almost always a legendary that gives you a huge bonus to damage reduction combined with set bonus reduction. Loads of builds also has other ways to not taking damage, like Stun skills.
They've already stated development on D3 is over. We'll probably see a couple of new legendary effects on already existing non-effect legendaries..but thats about it. ..Diablo 4 is more than likely in production.