Backblaze is not built to handle thousands of concurrent connections towards specific content, while both OVH and S3 are.
Amazon S3's Glacier storage tier is even cheaper at $0.004/GB/month.
And OVH's archive is $0.0023/GB/month. Although I guess that with archive storage, transfer and access costs could be a significant part of the bill. But OVH's business model is to be cheaper than AWS so I guess they'll end up below the AWS price.
Have a look at wasabi.
You also need to factor in Glacier retrieval fees and AWS's data transfer fees. Also watch out for extra fees for early deletion.