We reproduce fast.

No we don't. It takes at least 16-18 years for a human to be able to fight effectively.

e are innovative and we are moderately strong with the capacity of magic.

Basically the same reason every fantasy human empire exists

Warhammer and the Witcher does humans justice but manga rarely do. I've recently went through a 300 chapter Berserk binge(first time reading) and although Berserk is amazing, humans wouldn't survive in that world for a century, which is a minuscule amount of time in a geological timescale. Compare that to the crocs or sharks which survived for hundreds of millions of years.

Or even just some previous hominids that pulled a few hundred thousand year life spam before we ended them.