Bought my iMac 7 years ago with 8GB as the default memory option and a 1TB fusion drive. And here we are, nearly a decade later. Still 8 GB in the newest models. Still 1 TB fusion drives. GPUs haven't even seemed to take a jump over last year's models.
True. The only thing to replace 7yr old iMac is iMac Pro. I splurged, got myself one and expect to get another 7 yrs from it.
Why not get a 27" iMac for half price, and another one in 4 years with whatever new thing is invented then?