That's because you visited Istanbul, not Constantinople. Centuries have passed and it was thoroughly Orthodox at the time. Russia filled the bill in a tough time and now has Orthodoxy as its official religion once again.
We cannot deem ourselves worthy to be the spiritual center of Orthodoxy (the Fourth Rome, as you call it) if we do not first have a thoroughly Orthodox society.
That does not describe Istanbul I visited.
America isn't the spiritual center of anything other than greed and selfishness. We don't deserve the EP here for anything other than visits.
Facts are pesky things, but here I go, once again, to cite some relevant ones. America, to include her Orthodox jurisdictions, have a greater proportion of members attend church regularly and participate in parish life than any other country. Orthodoxy is the official religion in Greece, but in Russia it is not so de jure
, it just seems that way de facto
. (It is of of a handful recognized religions that are allowed to legally operate in the Republic, but not THE official state religion). Nonetheless, it was the ROC that gave us both thousands of martyrs and millions of victimizers/apostates. The ROC is on the rebound, thank God, but with 2% attendance rate and even smaller involvement rate, She has a long way to go.