I dislike how high the series elevates the importance of humans in the universe, especially in that episode.
That wasn't the point. The point was about Sinclair's own attitudes about what he considered to be important about human beliefs. Had someone else been given that task then they may well have just done holy communion or the Buddhist/Jewish/Muslim equivalent.
As for all the other worlds only have one religion, also not true. G'Kar named at least two other Narn belief systems (G'Lann & Na'Kili if memory serves) and background info written by Ditillio spells out that most of the League races have at least three major belief systems with distinct subcultures.
For all the attention the major alien races (Minbari, Narn, Centauri) earn over the course of the series, their depiction is rather monolithic. All the Minbari dress the same, all Minbari architecture is the same, etc.
Not true, on several counts. There are three very distinct styles of Minbari dress, one for each of the Castes. The Religious Caste are mostly wearing light coloured robes, the Warriors darker coloured clothes with studs and heavier material while the Workers have padded, reddy/orange coloured clothes in a more utilitarian style.
There's also a distinct difference between the architecture in Yedor, Tuzanor and the Temple of Varenni. One is mostly single large crystal spires with a blue tint, the other a more elaborately carved looked with a mostly green tint and the latter being very rough hewn, circular and made of rock, rather than crystal.
The Centauri palace on Narn is exactly the same as the Centauri palace on Centauri Prime. Much of this is due to budgetary constraints, of course, but that doesn't mean I have to like it.
Firstly, the fact that the INTERIOR of the Centauri seat of power on Narn was made-up the look like the Royal Palace was explicitly stated as a stunt to please the Emperor when he arrived. On the outside it was still a red, blocky Narn building, nothing at all like the Palace on Centauri Prime.
Diversity for the Minbari comes down to three castes for their entire species!
They're an old race with a declining population and have been a united people for over 1000 years. Still, it's established that there are many clans within each of the castes and that they don't all pull in the same direction, even within their own caste. The Wind Swords being the most prominent example as the warlike extremists. Even so, the uniting of all the castes and clans was something specifically done by Valen to stop the clans fighting each other. Also, to be fair, we've seen very little of the inner workings Minbari at a normal "civilian" level. All we've really seen is the various leaders and a whole bunch of civil servants.
The ending makes me groan almost as much as Delenn's line about how humans are special because "humans build communities." Please. But that's just my two cents.
Well, how do we know that this isn't such a rare trait among alien species? We take it for granted because humanity is all we know, so there's no way to make a comparison. Plus of course, that was only Delenn's perspective. G'Kar as I recall thought that Humans & Narns had more in common than he originally thought after reading Yeats. Londo had yet another perspective.
) about us being like ants not wanting to be stepped on, at least in the perspective of the First Ones. Really does bring a lot more to that scene. 
