The first rule of FMC usage is GIGO.
In the olden days, after the Earth had cooled but before the introduction of something which chipped away a little more at the need to think and which is called a "STAR", we would at some point prior to TopD examine the charts and determine the most limiting of the CTA steps (which protect against terrain) and plan a descent accordingly based on a 3X + [factor] angle to the limiting step. This was simple to do and kept us all out of trouble. The people who taught these techniques to the newer pilots had been doing the job for years and worked their way up through the airline. Pilots I fly with today look at this sort of thing the same way my dog looks at the TV. They used to call that concept "Experience" and in the olden days it was considered valuable, if intangible, by CEOs and managers who could see the wood for the trees but this is no longer so and we've watched certain airlines emerge staffed by inexperienced pilots eager to climb the scrotem pole and CEOs focused on share prices and dividends and woke agendas and gender quotas and so now with STARs and magenta lines to follow people scratch their heads and wonder how this sort of terrain event can happen.