@ThatCandidBear I’ve ready your posts and I think you are coming at this from the point of view that if a role is “full time” then it needs someone there 37.5 + hours a week. Rather than about the capability of an employee.
What you are confusing is presenteeism with capability. In my experience employees and managers are quite limited in exploring creative options for flexible working. This includes job design and redesign.
I have seen women be constantly rated as outstanding who go part time after having a baby and their rating drops to above average. As they increase their hours and go back to full time their rating slowly moves up to outstanding again. This is unconscious bias based on presenteeism.
Some people work 60, 70 hours a week - that’s not full time, it’s doing two jobs. We have some jobs that need 24/7 or even 07:00 to 21:00 coverage, which one person is expected to do by working unpaid overtime. Technology has played a part e.g. emails, mobile phones, the ability to be contacted 24/7. As has the drive for efficiencies and the bottom line.
Everyone should be given equal opportunity for promotion and the best person should get the job. If the successful candidate works part time, has a disability etc. then either the role needs to be redesigned to accommodate that or creative solutions like job share, reasonable adjustments etc. should be used.