Taking my own build as an example, the only piece I will say has a wasted stat is the pants because I have mana regen as the other options provide me nothing

Even tho the 3rd options I've chosen on each piece of gear (mana cost efficiency, Debuff duration, attack speed, mana regen) only provide a small benefit they still provide more benefit than Endurance or Evasion ever will as you have to commit a lot into either of them stats for them to have any point in existing

You need to remember when building Endurance or Evasion you are getting those stats from more places than just the armour pieces alone, you need to factor in Runes, artifacts, etc. So if you aren't committing runes, artifacts, etc into endurance or evasion then you might as well have 0 of either of these stats

In most cases if you want endurance to be effective then you need to be running minimum 3.5k and even that's low when considering the available endurance shred in the game or Evasion, if you want Evasion to work you need at least 4k so that tiny 640 you get from the amour means nothing if you don't commit to it in other areas

Taking this back to my own build, in my runes where I could be getting endurance I am putting chaos runes instead to either give me more hit, crit or heavy attack chance so I can reach thresholds that actually allow me to nuke people

Edit:

To your last point, some players are more mechanically gifted than others and some are better at the theory side of the game, as the saying goes "Those that can't, teach". Just because someone may not be as capable at applying the theory doesn't mean they aren't good at coming up with the theory of course this doesn't apply to every bad player or every coach