Does Jiren simply use brute force? Hit is a powerful opponent for Goku because he can use time skip and manipulate time and space.
Could this be said for Jiren, or is he simply an overpowered character?
I'm NOT comparing the two, I'm simply providing an example.
Jiren is not overpowered.

tl;dr More Power (KI) ≠ Stronger Fighter



The point of the character is to illustrate the difference of strength between powerful mortals, gods of destruction, angels and others we probably haven't seen yet. Jiren could be at a level between god of destruction and angel. The fact that he seems overpowered means we still have a long way to go until Goku reaches a level where he is considered the strongest.

In DBZ and even GT, Goku seems to be near to the level of all of his opponents before finally surpassing them. Super is taking a different approach. Goku and the others are struggling to even perceive the strength of their opponents. Other techniques and skills throw a monkey wrench in the idea of "more power = stronger fighter". Time skip, ultra instinct, and the energy of destruction are all examples of technique trumping raw power. 

The new anime is changing power scaling and what it means to be a powerful fighter. DBZ and GT relied on transformations to show a character was at a higher level. Super, like the original Dragon Ball, is pivoting to strategy and use of different techniques to show a fighter's skills are advancing.