To some of us, well, at least one, the Grills Terrace sounds much much nicer. I can see little to attract me in the cabanas, if only because they sound so claustrophobic with a view in only one direction. But I’m sure you would be able to achieve much of it on the Q1 balcony, if you have a remotely decent butler. Why on earth would you want a TV (of any size) when you can watch the sea? And on a calm day, there is the Grills Courtyard for dining, which some people enjoy. I usually find it a bit breezy.
What you also omitted to mention, which I think makes quite a difference, is how much extra the cabana is, on top of the already high prices.
But from what you say, I’m sure you’ll be disappointed on the Vista. 😀