How old is this? 80 MB will hardly load you a single web page. And how are you not going to burn through your 20 MB in random app updates, before you get to send a single text?
Some intranet site developed with React + Angular + Vue + jQuery + during development the dev tried a lot of packages but didn't delete the unused ones + no tree shaking + bundled all of the assets in the page
These amounts in the OP are BS, but 80MB for a single webpage is also not true. The rule of thumb for web development is to shoot for less than 2 MB per web page.
But look at the 20 MB option – it actually specifies a speed. 64 kbps! I think that's about a single browser tab on DuckDuckGo, which would take you 40+ minutes to load in...
No, it's definitely a data cap. For one thing, you're not getting gigabit internet, let alone giga_byte_, on a plane... but they also list the actual speed for the 20MB cap, a pitiful 64kbps. That's barely faster than dial-up.