There's a reason why groups are asking for high item levels. The majority of players who try to run it are complete garbage.

It took me several days of running Shinryu EX non-stop just to get a single clear, yet I pretty much knew the fight 100% after just a few attempts. When it comes down to it, Shinryu EX is really not a difficult fight. Phase 1 is easily the hardest part. But the problem is that a lot of players keep making the same stupid mistakes on Phase 1, regardless of item level. Yet all of Shineyu's mechanics are easily avoidable by any semi-competent player.

So, that is why people ask for higher item levels. It serves two purposes. It allows the party to skip mechanics, and it is the only real gauge with which you can somewhat check a player's competence. A player who only has an item level of 320 on his main class has probably never even cleared a boss in Omega Savage, and can't possibly be anywhere near competent enough to tackle Shinryu EX.