The OE, imo, is still a country that few (if none) can challenge on their own. Their ability to expand into AI territory, which is conected by land to Instanbul (their capital), gives them tremendous MP, decent wealth, and awesome census taxes.
They are the bane to many a nations, specially to Austria/Russia early on (if OE decides to turn into a greedy bastard). Spain rarely matches the OE's ship supply limit, even if it owns all of italy.
Properly played, specially early on (till 1600's) the OE can be unstopable. And its not one war, or 2, that are going to finish em off. Unless you are evil enough to take the straits near Instabul, to cut em off from a majority of their MP and a good slice of their income.