I was worried about the performance of GT7 on the PS4, but it works well enough and I have an original spec PS4 that's been rebuilt. It has the OEM hard drive in it too. It likely doesn't look as good as the PS5 and the loading times are longer, but overall I don't think it looks any better or worse than GT Sport does.
Would I buy a console specifically for the game though? Nope, but I don't think I'd buy a console for any one game. However, with that said, there are still plenty of good games you can play on the PS4.