One dimension to consider here is cost of compute. Going from 8 hours to 4 hours is a 50% reduction in the time to compute and we're assuming this is occurring

One dimension to consider here is cost of compute. Going from 8 hours to 4 hours is a 50% reduction in the time to compute and we're assuming this is occurring on the same relative hardware/instance size. At scale, that could translate into hundreds of thousands of dollars in savings. But your points are relevant - as with anything related to development, "it depends" rules the day. There isn't a clear cut "x is objectively better than y" in general.