Not all modern panels have ‘smart’ features, and those that do need not be used. Your use case is literally changing the source on the TV (smart or otherwise) to various HDMI inputs.

Older panels will offer worse image quality, be larger and heavier, likely consume more power (especially in the case of plasma TVs), and not have features that will improve gaming experience such as game mode to reduce input lag, upscaling to improve image quality especially for the X360/PS3 generation, and some sort motion-interpolation like Samsung’s Game Motion Plus especially for 30fps games.

There is no benefit to getting older panels for your use case, except perhaps cost benefits although modern panels can still be found for very low prices. An older panel will not provide any sort of gaming advantage simply because it was manufactured around the time of a PS3 or whatever.

I doubt you can really buy those TVs anymore without it being a “Smart” TV. The best you can do is disable the Internet Connection on your TV. I have heard couple people suggesting commercial TV but I’m not too sure how great they would be for gaming and more made for well… staying on most the time, inside at a shop.