I know we're just arguing about amounts at this point but that's pushing $2M a week. It seems on on-prem would make financial sense long before that.
Depends on your requirements. If you need 11 nines durability S3 is probably still cheaper
There's also the hybrids. Only storing "unlikely to be accessed" data on S3 would likely remove a huge part of the AWS bill, while significantly limiting the size of the on-prem data set.
Of all the possible related problems, object storage is the easiest.
I really hope that Canva's executive dont believe their product need such garantees…