So why aren't these Mary Sue assholes running everything? Why Do humans outnumber them so heavily? Is it that they are dying race and humans are too prodigious? Is the magic of the world fading? Well, maybe a little bit, but no, the great limiting factor is biology.
As with Dwarves I am a fan of using biological limitations or quirks to explain why a species would fit to fantasy tropes. For the city dwelling high elves, the solution seemed simple. They are pescetarians who cannot drink fresh water, they require brine as humans require fresh water. With such a little change it makes perfect sense that they would seek to dominate the waves but wouldn't bother with inland holdings which would be difficult to supply. They no doubt have some in strategic locations, but by and large they can't afford to set up a city in the desolate brine-free forests of central Europe, Asia, or Africa. Their territorial control of the oceans also explains why the presence of magical spells doesn't enable more trans-oceanic contact and trade. The ocean is full of elves with better ships than you can cobble together.
Other bloodlines of elves, seelie and unseelie or any other magical creatures exist too (like Barbarians). But these fill the role of snobby "High Elves" for me, things that exist to leave ruins of once important strategic locations without really interfering in the day to day of dung age mortal affairs. High Elves are something "out there" in the oceans