So now there are two shoeboxes. Hasn’t solved exfiltration. In fact, you’ve just doubled the risk.
There may not be a solution if the problem is untrustworthy people.
The custodians of your ‘independent control’ will eventually get ransomwared themselves.
Then what?
It’s like cash...
If you are a sophisticated criminal, do you waste time burglarizing individuals? Or, do you rob the bank where the individuals keep their money for ‘safekeeping’?
How many people at Amazon have access to the database other companies use to store info?
2?
20?
200?
I don’t know, but I bet it’s a lot. And I doubt they get paid enough to make them immune to a generous offer (or a scary threat) from a bad guy.
Seriously, how many individuals at Amazon have the ability — if they wanted - to irreparable corrupt, encrypt, or destroy data?