I prefer any iPad Pro or any other latest iPad with 8 TB of add on storage. Easier and more options with lower storage but I know it is by design just dislike you never get that exact amount. It the nature of formatted storage. Even if it is onboard storage. You can not even go over 2 TB so no way possible to get 8 TB or somewhat less of onboard storage yet. Yes it will happen but when ?
Onboard and add on storage are both portable. Biggest advantage of onboard is it can never disconnect from port. Not that big of a deal. At least with add on storage you can use it on two, three, four, or however many mobile devices at once. Instead of having to have copies of everything tons of times on each device. Would be waste. Doubt that would ever happen but if so.
Sure you could save a lot and not have any local storage with onboard or add on but I guarantee no mobile connection will stream high quality 4k video without any buffering no matter where you are. Unless you determine the exact spots to be for optimal streaming performance. That is impossible way to many factors. It can change every second, minute, and day.