Lunaruse
The Milkdrinking Elf
I don't particularly believe in elven supremacy, but neither do I believe that Tiber Septim became a god. Judging by the long life spans of most elves, I'd say that they most likely knew him, or knew of him before he died. And if there are elves walking around that are older or as old as a god, then it makes sense for them to go 'whoa, wait a minute' when people start declaring Septim a god.
I think because Tiber Septim was both a Nord and an Emperor, he was accepted, in general by both Nords and Imperials as a ninth Divine. Elves would believe in their superiority, because, as you said, many of them might be a good deal older than Septim. One wonders why it would start a war to ban his worship. After all, there are eight (8) other divines to worship, none of them exclusive to elves or men.
I don't think you are viewing their motives in the right way. They didn't start the war to ban the worship of Talos. They want to destroy the Empire and the banning of Talos worship is merely a tool to help get the job done.