Your frustration is understandable. But there are alternate lessons you can take from this.
First off, yes, in running, talent is a factor, and talent can be monumentally unfair, just like your coworker being the boss' son can be monumentally unfair.
That said:
1. If you're working hard, you're in the mix. That means you're in a position for luck to strike. (See: upset race results throughout history.) Best you can hope for in some situations if you weren't gifted with privilege or don't have any air cover at work.
2. But there's a further lesson you can take from running, and from this existential moment you find yourself in, which is: You've just realized that you need to be more strategic with your hard work.
In running, if you're built like a distance runner but are training to be a sprinter or shot-putter or whatever, you're just not going to get a top-tier performance because of sheer biomechanics and physics. Unfair? Sure. But wishing it were otherwise is just wasting energy, and maybe any potential you have. Sometimes it's more productive to ask yourself if you're competing in the right arena.
Alternately, if you're training for a race and do nothing but intervals, rather than a strategic 80/20 mix, your results won't be optimal and you'll just burn yourself out. Which sounds like where you are now.
That great "Why I Sucked in College" essay on this site contains a passage I think about all the time, especially as I age: The point of training isn't to run hard — it's to learn to relax while running fast. That principle applies to a lot more than running, in my experience.
I mean, also, life can just be merciless and suck, but at least exhaust your strategies before throwing your hands up in despair.