Philosophical view on backups: The ONLY purpose of an off-site backup is to recover from a major disaster; theft, fire, flood, etc. See below:
Most backups - except for the last couple days - should be on site.
The reason is that IF you have to recover a database, the LAN is always an order of magnitude or faster than your WAN connection, and local disk is another order or magnitude faster yet.To recover from off-site storage can be time consuming and business expensive.
As such, the mandatory off-site storage should be the last 2 days. 1 day is insufficient, as you may have one of these major catastrophic disasters in the middle of a backup, which would negate both in house and off site data integrity.
Yes, there might be a reason to off-site other intervals - say month-end, but in general, running data off site that will never have value, is a waste of resource.
Backing to S3 has advantages, but with one advantage that should also be applied to in house backups as well. Backup to an operating system other than the one that the server is on. Not foolproof, but almost every Ransomware attack works by encrypting the disk at the OS level, Having the backups on a different OS, provide a "potential" insulation factor that may protect your data.
There is no electronic data storage on the planet that comes close to the resiliency of S3, but that does not mean that the data shipped up to S3 is, in itself, valid. Running a disaster recovery exercise would be prudent, to insure that the integrity of the stored data can be effectively recovered.
It would also be best if the local backup was on a WORM device (Write ONCE, Read Mostly), so that once backed up, it is impervious to malware/ransomeware attacks. Tape is a good, cheap solution to that issue.
Point-of-time backups are essential (your retention policy). I had a $20B client come to me about a backup issue. They ran daily backups, but with no retention of point-in-time historical records. A creeping data corruption issue was discovered (not FM), that went back to some indeterminate time in the past, Millions were spent to attempt to piece back together past data. Very painful.......