ps4 is 1.84 tf, 7850 is 1.76tf, 7870 is 2.5tf and 7970 you compared is 3.78tf
Good. These are also early 2012 products, and most likely dont see much attention support wise in current games. Even though said that, they still tag along fine if your content with base-ps4 settings and the occasional bad port regarding last generation games. Also, 2gb can only do so much when a game is designed to eat 3gb or more vram. its quite the difference looking back at 6th and 7th generation, PC gpus aged much worse there. Could be due to the move to X86, the stagnation of hardware improvements/moores law, better scaling or a combination of those things.
Edit: anyway, ontopic (this isnt the retro topic)
1080p/30fps if you want the highest settings (quality mode)....