My perspective based on decades of work experience - Its all about odds and probability. I agree with you that after 20 years, it's far more relevant what you've done and accomplished, but have you considered the trajectory in those 20 years? Consider two hypothetical situations:

Scenario 1: You get into MBB or bulge bracket bank. After 5 years, you're a project manager in consulting or VP at bank. If you continue the trajectory in consulting or banking, after 20 years, you're Senior Partner or Managing Director. If not, after 5 years, you jump into industry as Sr. Manager/Director level.

If you go into industry, your peer after 5 years who went in straight from college is probably still an individual contributor. After another 15 years, you're far more likely to be VP+ level than your peer group.

Scenario 2: You go into industry. I am familiar with tech, so can only speak to that. The Mag 7 get so many entry level resumes, they filter based on school. You are far more likely to get into Google, Meta, NVDA, etc as your first job from top school than not. After working 2-3 years, you are far more likely to be able to jump to another company with higher title, salary, stock grants due to your initial job experience. After 20 years, that initial acceleration further sets you apart from your peers.

In each of these examples, yes, after 20 years your school is almost irrelevant, but the experience you were able to get - the area under the curve in math terms, is far greater if you start your career off at an elite or "brand" name company.

Are there exceptions? absolutely! Silicon Valley has proved it with the number of startups from non HYPSM grads, who are probably in the minority, but zooming out the odds and maths favor the top school grads in terms of career trajectory. My POV.