[doikor]

Now try to hire 20 level designers and 5 engineers who know how to work with your engine/tools.

Same applies to most software. It isn't that hard to make a new programming language or a http framework. But once you make one finding other people who know how to use it is a pain in the ass.

[bennyschmidt]

Level designers use tools, not really contributing at the game engine level. Long before I built Shadowvane I built a map editor in Three.js that anybody could use. If the game became profitable, in-house tooling would sophisticate and the team would be the ones shaping it. But yes if for some reason my first hire was a level designer, they could add value day 1.