For example, imagine you want to keep a smart TV offline but you also want the latest greatest eARC features over HDMI 2.1; or you want that new Dolby tech to work with your PlayStation 5. That's stuff that came out in the last couple years. Assume it will take the TVs five years to work seemlessly. In the meantime you're gonna need firmware updates. It won't work out of the box. Or maybe it will, but with a noticeable lag.
Whatever smart TV model you're considering, read the patch notes and visit the fan reddits so you know what you're getting into.
An alternative is to get a gaming monitor; however these rarely reach TV screen sizes so if you're looking for 45"+ you're stuck with smart TVs