iLvl gear has it's pros and cons...

Pros:
1)You don't need to grind on every job for another 20 levels (well over 1 million exp per job) to reach 199.
2)You don't need to skill up another 242 levels of skill for A(+) level skills (even the thought of that for summoning magic makes me shudder!).
3)Some weapons with multiple jobs instantly boost all of those jobs by 20 levels and 242 skill. Even with a grind to accomplish getting some of these weapons is better than that grind of all the exp and skilling up.

Cons:
1)Some non-ilvl gear is still not only useful, it's irreplacable. EG. Casting Sentinel's Scherzo in full aoidos' +1 gear will give you the most potent damage reduction that you can get, along with an extra 5 VIT. Sure other pieces can extend that duration, but you lose some of the potency and/or VIT.
2)Using said non-ilvl gear on lvl 119+ content can very easily get you 1-shotted. And that's not fun.