I guess it depends on how likely you are to need to do that. Looking at b2 vs glacier deep it seems as long as you don't need the data more than every 2y that glacier still works out cheaper even with the high bandwidth costs.
But glacier also has minimum storage duration. With S3, you'll need to use a tiered system unless you want to store all backups for several months (often that's only the case for weekly or monthly backups).
In the end, S3 can be cheaper but you have to make a lot of assumptions beforehand. Backblaze is cheap enough to just throw everything in there and work with their lifecycle rules. You don't need to make assumptions about download volumes or storage duration beforehand (esp if you can retrieve via cloudflare).
