Tarsnap pricing is for deduplicated data. You need to divide it by orders of magnitude for a proper comparison.
To be fair, that depends on how much duplicate data you're backing up. If you weren't using Tarsnap, you probably wouldn't have very many mostly-duplicate archives.
I think the better way to look at it is that Tarsnap makes it easy to have many archived snapshots of your data without paying very much more. Whether being able to have daily snapshots for the past year is worth more than always having just your latest archive... well, that depends on what you're doing. It's a feature I think is important for my own use cases, but I'm not so bold as to think that everybody has exactly the same needs as me.
To be fair, that depends on how much duplicate data you're backing up. If you weren't using Tarsnap, you probably wouldn't have very many mostly-duplicate archives.
I think the better way to look at it is that Tarsnap makes it easy to have many archived snapshots of your data without paying very much more. Whether being able to have daily snapshots for the past year is worth more than always having just your latest archive... well, that depends on what you're doing. It's a feature I think is important for my own use cases, but I'm not so bold as to think that everybody has exactly the same needs as me.