It’s not a bug.None of them have been that large. If you can get to storage quickly enough you’ll see the actual size. Very small compared to what’s shown in the update. It’s assumed to be a bug. Regardless each one downloads very quickly and installs just as fast. Only my initial 26 install took any time.
Your phone downloads more files than a binary with the exact changes specific to your device config. Once the extraction is complete all the redundant files are discarded so what you see in the storage is the final delta that’s actually applied during the update process. It’s how it’s been done for as long as I can remember.