I am talking here about 7.5M addresses/keys per one wallet.
How is Bitcoin Core handling that? Can't you just let it sync and see what it shows?
Dumpwallet would be ok if it could only dump private keys of used addresses/keys.
I haven't used it (and don't want to test on my wallet): what does the output look like?
Bash no because it is too slow.
A few million entries isn't a problem in bash. Getting only addresses from a long list is very fast with
grep.
I have csv files: transactions, balances.
Only have to connect transactions and balances with public addresses/private keys.
What are you looking for? Addresses with a balance?