While having a plan is important, it's not the only way a human approaches chess. Experienced chess players develop an ability to evaluate positions intuitively. Without being able to explain fully why and without a specific plan in mind, they're able choose the best position out of several options. In a way, it's very similar to a evaluation function without access to its internal logic.

> All it does is mechanically keep on steering the game towards positions that are evaluted as best by the function.

I wouldn't say so entirely--It's possible to predict multiple moves ahead (before the number of possibilities explodes), and a heuristic is a sort of plan too.

What you're describing sounds like a greedy algorithim more than anything else.