In the past(BC/Wrath/Cata) the difference between honor gear and conquest gear was 13 ilvl, and it was even less since the gear lacked one sub-stat. Now there is even more disparity between gear of same ilvl difference because now gear upgrade increases main+2sub+power+resil.
Now in Mop the gear difference is just too huge; comparing the ilvls-
The difference between honor and conquest gear is 25(19), and counting upgrades 33(27).
The next season's would be
458-476(483)-493-515-523(with upgrades back)
so the difference between honor and t2 conquest is like 39(32), and with upgrades 47(40)
Basically we are having a whole expansion's worth of gear difference in just a single season.