It can go worse - some cheap and badly designed Android phones which download updates from every month when you first buy it until the current month, so maybe 10+ updates, but they aren't deltas (diffs) but full images. Ridiculous on so many levels.
It is a complete image, but phones today have nontrivial state that may be a problem - e.g. your baseband processor might have its own rom with its own update protocol, which changed between image 2 and image 7, so image 10 after image 1 will be unable to update the baseband.
I honestly consider that a pretty reasonable trade-off.