Microsoft made sure in windows 10 that it's almost unusable without SSD. SO you big binary blob file have random r/w access.
Most backup software is able to do good binary deltas of arbitrary data for decades. Even dumb checkpointing resolves problem of downloading 25 versions - you download latest checkpoint and deltas from there.
Don't excuse poor design and programming, when you know a file structure, creating a differential update should be short task. With a tiny bit of algorithmic knowledge you could even optimize the process to only download needed assets inside of you big binary blob - if the asset was changed 7 times during your last 25 version you only need to download the last one.
I'd personally like to see a company put a little thought into innovating how they store data on disk so patches can be quickly applied like with git while also not requiring a full source recompilation.
Not all versions are made equal either - one might be a character buff, another might reorder assets in the "big huge binary blob file" for performance improvements. At a certain point, rather than downloading 30MB per update for 25 versions, and applying each incrementally (remember that you have to do them in order too), just download the full 1GB once and overwrite the whole whing.