First, most/all new Smart TVs are doing automated content recognition, collecting and sharing details about what you watch with the manufacturer, which they sell and/or use to show you ads. My understanding is that most new Smart TVs are showing you ads regardless. I'm opposed to this on principle.
Second, at least the Smart TVs I've personally used (a couple of Vizio sets, a late-00s FHD Samsung, a mid-10s 4k LG) all have really slow and unpleasant UIs. The Vizio in particular was glacial, and I couldn't understand why the set owner even bought it (they were only streaming through built-in apps). I'm guessing newer and higher-end sets are fast, but I haven't used one myself.
And finally, I don't want an integrated device like this anyway, I would prefer to pair a really nice panel with a separate smart device (roku, apple tv, linux, whatever) so I can upgrade those independently. If I am buying a Smart TV with no intention of using the smarts, I feel like I'm either paying too much, or not getting as nice a panel as I otherwise could.