I don't get how you can say both their shikai are irrelevant. Shunsui's ability makes children's games a reality. In other words it's minor warping of reality.
No, not even.
He can't be harmed except for the color called in irooni
It's not that he can't be harmed, it's just that the damage is minimized. And that's only if he calls out a color that doesn't exist on his body, but does on the opponent (in this case, it'd be blue or green). The problem is that it's a one-strike limit, and then it's the Admirals' turn to call their color. Aokiji can bypass Irooni anyway with his freezing. And I can guarantee you that given Kizaru and Akainu's long ranged, spammable, attacks (each of them capable of one-shotting Shunsui) against Shunsui who's limited to close quarters combat, Shunsui will not even have the chance to cut the Admirals while it's his turn.
And even if he does land a blow and inflicts massive damage, that can be patched up by their logia abilities.
The only thing Irooni can do is literally extend his life by a few seconds.
Takaoni kills whoever has the lower ground,
Do tell me why you think this.
bushogoma is a top (mini tornado),
A weak and useless one, seeing as it's only good for distraction. Any of the Admirals can plow through it with raw strength alone. Shunsui only used it so that he can use Takaoni, but seeing as the top part of the Bushogama is completely open, anyone could easily escape the tornado by moving up and launch something at Shunsui to interrupt him.
kageoni allows him to become the shadows
Getting within arm's reach of the Admirals is a bad idea. Especially seeing as Shunsui can't severely injure them. And this is assuming that the Admirals are standing still and are touching a surface.
Saying that the Admirals are somehow exempt from Shunsui's ability and not being bound by the rules is like saying nobody would be bound to Law's room rules.
Nowhere did I say that the Admirals are exempt from his Shikai. It's just that his Shikai is useless. Useless in that it's ineffective against the Admirals and it's not advantageous for Shunsui.