Except, how many progression groups have the luxury of multiple full i90 members? Sure, if your group has the fight on farm you can probably get it down to full darklight + santa caps and winning.The real use of gear is to lower difficulty for your group. Everyone does their best to contribute the most they can. As a tank, I do my best to take as little damage as I can. Besides, pld is my main, I want to grow as far vertically as I can on it (you have said you have a different priority, I don't expect you to play the same as me), now that my vit is as high as it can go, the only space left to grow is secondary stat maximization. My point was simply that yes, the primary factor in any tank (or healer or dps) efficacy is their main stats (vit/str/mnd/dex/int), and that even perfect secondary stats might not be a huge increase.
All I am saying is that while secondary stats are not essential to be effective (or even "out geared") they are not "negligible" entirely. For those people who wish to grow their main class, secondary stats are a viable and meaningful way to do so once you hit full i90. Again, as I said before, I will not argue that you "zomg must max parry or your awful." But I also won't accept "zomg parry is pointless just max vit and everything else is dumb."
I identify with your desire to level other classes (personally I'm at war i85, brd i79, whm/sch i76 and drg i76 and growing). We just come from two different play styles. Some people will always want to max as far as they can vertically on their favorite class, and the gains those people achieve will be relatively small but still present.
As a mathematical aside, 2-3% mitigation over time isn't as small as it sounds. Ex: Pld's Rampart is 20% for 20 seconds every 90 seconds, or 22.2% of the time you mitigate 20% which is 4.44% over time. Similarly Sentinel is 2.2% over time and Vengance is 3.75% over time. So those "small parry gains" are actually pretty strong over time, effectively giving you an entire extra cool down.