an x64 laptop that can run anything

That used to be true, but simply is no longer the case. Commercial streaming services are heavily restricting how and what you can output on your x64 PC.
You’re not only getting far better platform and format compatibility on your cheap Google TV or Fire TV stick, you’re also getting the far better apps and overall user experience.

That’s also nothing stopping you from installing Firefox on these devices or pairing a mouse with them, if you desperately need “browser plugins” and an less sofa compatible input device for whatever you’re doing in your living room.