The simplified model that leaves out tricky implementation details is just "every file that's different is a different blob object, stored in full on its own, under the hash of its contents". If you work with this model, you're basically correct in all your reasoning, except that in reality a bit less storage is used because some objects get packed. If you work with the wrong (wrong! not simplified, wrong!) model "every blob object is stored as base-and-deltas", you won't reason correctly about either how the object store presents itself in plumbing commands or how it's stored.
I never said that Git commits are diffs. Keep it civil.
> The simplified model that leaves out tricky implementation details [...]
Models do that.
> If you work with this model, you're basically correct in all your reasoning, except that in reality a bit less storage is used because some objects get packed.
That's it? That's the one detail that should stop me thinking correctly based on this model?