I'll post this anecdote for anyone who might find it useful. A few months ago, my elderly parents switched from Dish for TV and Comcast for broadband over to YouTube TV and AT&T Fiber. Now, with fiber they get unlimited data, so it doesn't matter how much data they use with streaming. But I was curious what their data consumption would look like now that all the TV they watch is streaming. They're not the types to leave the TV running in the background all day, it's only playing when they're sitting down watching. Between their two TVs, they probably stream an average of 3 to 4 hrs of TV per day. And then there's the other stuff they do: web surfing, home phone (VOIP), streaming music on smart speakers, email.
They tend to use around 400 GB of data per month. Some months it's less, some a little more. But in their first 6 months or so on AT&T Fiber, I've never seen the total that AT&T tracks hit 500 GB once.
Obviously, depending on how much TV would be streamed in your home, switching from traditional cable/satellite to all-streaming TV might mean that you need unlimited data. But that's certainly not true for everyone. In places where Comcast has a data cap (like here), it's 1.2 TB (i.e. 1,200 GB) per month. My parents aren't ever coming close to half that amount, even after switching to YouTube TV. So if for some reason they switched back to Comcast for broadband, the data cap wouldn't even be a concern for them.