You need to think of it like a platform. The chassis looks the more or less the same from when it was first launched, but the technology that is attached to it, got upgraded with time. Better avionics, better weaponry, better sensors. It's really a modern form of ship of Theseus.

t. worked on the F-15.

Soon we’ll have some 100 year old B-52s in service in the 2050s with the re-engine program. The actual airframes will not be 100 years old, but same design.

That top Pic is more like 70 years old.

We need a new era of 0 to 1 inventions. We've had enough of 1 to n.