"So the 747 essentially is a 1960s design meeting 1960s safety standards."
I think you would be hard pressed to find many individual Regulations within FAR 25 with an Amended Date in the '60's. Case in point - the 737 NG - though a Derivative Certified under FAR 25 - still ended up with WET Certified Takeoff Performance Numbers.
It's a bit of a stretch to say that because some parts of FAR 25 originated in the '60's - even though it has continuously changed - any airplane Certified by it is a 60's vintage A/C. It's an evolving document.
BTW - I don't intend to imply that FAR 25 is a perfect document.
Regards,
LK