No, that’s not true.
Before teaching, I worked in the private sector company that had a defined benefit scheme.
It swapped from a ‘final salary’ scheme to a ‘career average’ scheme while I was there.
Take a 60 year old senior manager. In a defined benefit final salary scheme, the ‘defined benefit’ -ie the amount of pension paid - was based on their final salary. So if they finished on 100k, then their pension defined benefit was based on 100k.
However, another senior manager retiring at the same age and who earned 100k until the final 2 years, at which point they stepped down into a lower and less well paid role in the company due to caring responsibilities, would be paid a defined benefit pension based on that lower final salary.
In a ‘career average’ scheme, each employee ‘buys’ a bit of pension each year, based on their salary that year. When they retire, they get a defined benefit pension based on that ‘career average’, whether they finished in 100k or 50k or 20k.
Defined benefit simply means ‘you know what you will get’, rather than it being based on the vagaries of the stock market into which your pension money is invested. How that defined benefit is calculated can be ‘final salary’ or ‘career average’ or, presumably, others.