When do we just fix airplane design assumptions to match the real world instead of forcing the real world to comply with the "reasonable" assumptions of the eng

When do we just fix airplane design assumptions to match the real world instead of forcing the real world to comply with the "reasonable" assumptions of the engineers / aircraft firms. I'm almost a full stone lighter than the 75kg assumption, but I'd never walk into an office and just say I'm average, lets just assume that when designing. That is garbage engineering. Your built in assumptions should include projections that cover the expected lifespan of the product, not what is average in the here and now. A simple regression fit would be better than nothing. We should better plan for the extrema of humanity as to not implicitly dehumanize people with averages. That just blows.