Well, I would argue that Sinclair is more influential/important/revered to the Mimbari race than the human one. He after all was deeply mistrusted by Earthforce after his capture effectively ended the Earth/Mimbari war and didn't have the success or acclaim that Captain Sheridan did for instance.
He also did not play a pivotal role in the Shadow war or Earth civil war. He may have been "Ranger One" but that was always a behind the scenes post where fame & recognition was discouraged. Also he was only Ranger One for one year & then Delenn took over the role during the "important" years and later in the formation of the Alliance. Sinclair's achievements are in helping the Mimbari in the previous Shadow war & setting up their government & prophecies for the "war to come".
I suppose ultimately it boils down to the fact that "Sleeping in the Light" was set 1,000 years after Babylon 5 and
after Sinclair had already gone back in time.
If it's any consolation, the Mimbari love him to bits
