The bitrate of 4K from streaming services like Disney and Netflix is much, much lower than your UHD Blu-ray rips. They recommend having a 16-25 Mbps connection to stream 4K, but the average bitrate is even lower. It's closer to 6-8 Mbits. They just recommend a higher Internet connection because of how streaming works (small bursts of higher rates with a lot of idle time in between).
You can calculate it accurately by just downloading the movie (if the streamer lets you, like premium subscriptions do) to see the file size, and then dividing that size by the length of the movie in seconds. That will give you the average bits per second by definition. You'll be surprised how low it is, because streamers use compression, while "pure" UHD Blu-ray avoids compression to satisfy purists.
As to how much data a streamer uses, it's immense. It's a huge chunk of the data on the Internet at any given time, with estimates in 40-60% range for all the streamers in aggregate. Look into "Content Delivery Networks" (CDNs) to see how it's delivered on a global scale. It's actually very impressive.