I thought QoS is disabled by default. Isn't it? 350-450 mbps is just the powerline rate, it's different from the internet speed. And the powerline rate may not be enough. If you have AV500/600,...

It's odd. Update firmware of your powerline, contact tplink support if no luck.

How do you see they cancle TL-PA9020P? I see from the website that that model is still active.

That's strange. Did you set any filtering on your router that only allow the old PS4 to connect? If not, better contact tplink support again to get to the bottom of it.

Usually range extender is compatible with most of routers. Troubleshoot first: https://www.tp-link.com/en/faq-2234.html If problem not solved, contact tplink support.

Connect PS4 to the Ethernet port on RE200 if possible. Playing games usually required high bandwidth. Connect it directly to your host network, check if that works fine.