Solving the "elf superiority problem"

[King of Nowhere]

Ok, it's more than just elves. But the issues surrounding long-lived creatures abound--

* If elves live 7-800 years and mature (physically and psychologically, if not socially) by ~50-100 years, why aren't they in charge everywhere? Why aren't they all experts in just about everything? After all, one of the big issues with current scientists is that by the time you reach the frontier in your field, you're already past your most innovative early years. But if you have another 600 years to go...and things like dragons are even worse.
* If they only mature at the same relative rate as humans, then survival goes way down.

I'm not happy with the "oh, they just don't breed fast for...raisins" explanation. Or the "they're all such perfectionists that they take forever to learn anything."

I also, as a matter of setting, don't want to make immortality a cost-free thing. It's a major setting constraint--everything has tradeoffs. No free lunches anywhere.

So I came up with the following explanation to resolve both things, as it turns out that immortality is just a special case of really long life spans.
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Key Principle: The ability to change and grow, to innovate is a consequences of impending death.

this is a perfectly fine worldbuilding principle.

myself, i used different life spans as a source of conflict.
humans resent elves because they tend to take up many leadership positions. elves resent humans because they breed much faster and are taking up all the space
elves see humans as cursed with a quick death. humans see elves as retarded who need a couple decades just to learn to use a privy.

in any case, longer lived creatures breed slower because they have longer pregnancies and longer time for children to reach maturity. a human woman can make a children every year. an elf woman will need over 5 years before another pregnancy. and goblins can make three children every year easily.
In fact, the answer is not "why the long lived races do not take over", but "why don't the fast breeding races take over".

as for dragons, i solved it by making them dependent on their hoard. something about them needing to absorb magic from the environment to sustain their physically impossible exhistance, and the hoard concentrates magic. the bigger the dragon, the bigger the hoard they need, or they'll die of slow consumption. the dragon population as a whole is limited by how much loot they can get