So the default was that the mining reward of 50 BTC was sent to a different public key each time?
It would favor the scenario of "gradual breaking" the keys rather than "grab all at once".
Correct.
The public key with the largest amounts of coins stored in a P2PK output that I am aware of is:
04633280c0a93b45217059013ddadab8d35b9a858336028fecdff64c6a5e068fadaf7d2b73bc22795fa160c2304703320516e1b0b20e43d613fa5975787c8287e4
This corresponds to the following uncompressed address:
https://blockchair.com/bitcoin/address/1PTYXwamXXgQoAhDbmUf98rY2Pg1pYXhinNote that all the dust outputs which follow are P2PKH outputs paying to the address, not the public key. Only the very first output is P2PK, meaning 3,233.17 BTC are locked behind that public key.