First, you're not paying TWICE for the game. You're not paying 60 bucks, and then another 70. You pay 60 to play on the PS4 and 10 more if you also want to play on the PS5, taking advantage of the hardware.
Second, you can still play the PS4 version on your PS5, via backwards compatibility.
I get it, it's not an ideal scenario, and yes, Sony is greedy, but it's also a falsity to claim that you need to pay TWICE (full price each time) for the same game.
EDIT: Come to think of it, why didn't anyone bust a but when Sony released God of War III for the PS4 with better resolution and framerate for full price? Why didn't anyone demand that people who bought God of War III for the PS3 should get the upscaled version on the PS4 for free?
There is no upgrade path from the $60 PS4 version at this moment. There's only a dual entitlement version for $80.
at least try to have a basic grasp of the issue first.
Also, your edit comparing it to the GoW III situation makes no sense. God of War 3 PS4 was a remaster that came out on PS4 after the PS3 release.
Horizon Forbidden West PS5 is being developed along side the PS4 version, and both versions will go gold around the same time. same day release. No extra effort.