Employee level vs Design/Tech Rating

I have sometimes come across situations where I had to fire an employee to hire a new one with better tech or design ratings and more research/speed points. However, since the earlier employee had been with the company for quite a while, the level of the employee was higher than the one I hired (say, level 6 against level 4).

Are there any specific weights given to the employee levels and design/tech ratings? If yes, which of them is more important?

(Assuming budget factor to be same.)