Bah, so it's *yet another* layer of RNG to deal with. This game's RNG layering is ridiculous.
So I guess this means my level 50 set just happened to grow a lot more optimally than the level 70 set.
But also keep in mind that the main stat will always be better on a higher tier set and it is not random. So for the right side it makes a big difference, i.e. an attack% boot will cap at 50% main stat for 70 tier gear and cap at 65% for 85 tier gear. 15% more attack can pack a wallop and make up for poor sub-stat rolls. If you upgrade from 70 to 85 on all right side gear and are going for, say all attack%, you could see a 45% increase in attack. On the left side, since main stats are flat it is less important. I try to stick to 85 gear on the right side when I can, unless I'm specifically building for speed and don't care as much about the main-stat. On the left side I have tons of gear that is still like tier 67 just because the sub-stats rolled so well.