The ISO to do a full reinstall of Windows 10 is a bit over 4 gig, if you are rebuilding a domestic machine and need a few other drivers and apps you might get to 5-6 gig. Even on a limited plan that’s about 10%. There can be problems though, as others have noted, if downloads fail in some respect and are repeated. Yes there are solutions to this but they are not suitable for everybody.
My view is that Microsoft give priority to updates in a way that conceals and ignores the cost in downloads so many will not be aware that there is a problem much less know how to deal with it. We have not yet got anywhere near auto-everything software nirvana.
If the Poli using 300 gig a month on a pricey connection wasn’t streaming video for personal use I’ll give a pig to the church.
“Our aim is to make computers as easy to use as washing machines” - attributed to Bill Gates. People imagined he meant computers would be made simpler, actually it was achieved by making washing machines more complex.