The lagginess is a puzzle to me; one big selling point of the Roku (vs. e.g. the Amazon Fire Stick) is that it is so much more responsive, but newer models have been getting worse instead of better.

The last time I used Apple TV I was disappointed, and since they are a streaming provider themselves I expect this to get worse rather than better. Even very basic UI things like "what block in the UI is the cursor currently selected" are painful, and the navigation flow mirrors the navigation flow of the Apple TV app on Roku, which is already pretty bad -- navigating the a series page from a single episode is a tortuous multi-step process that involves getting the incantations exactly right or being reverted back to the main screen and losing all context.

The moat here is mostly just having widespread and maintained support for streaming services, which is a question of scale; that's why so many "Smart" TVs get stale after a year or so while Roku stays fresh. In 2008 I paid (in 2008 dollars) $99 for the Roku. The price now is much lower but I would probably be willing to pay that amount for a fresh device that is performant and agnostic to streaming services and no ads (including those remote buttons) and has a straightforward UI.