Since I sent it directly to coinbase.com and they own those private keys, would it be possible that coinbase is leveraging my hash with high rate fee to get other low rate fee hashes confirmed?
This is the hash id b5411a3c59d1472b5627b423355564cc26fc1345fee435f0665299f637c1d286
Let me make it clear to you, Coinbase is the receiving end here so they are not doing anything and neither will do anything to push your transaction. The one who told you that they send you funds from confirmed TX doesn't change the fact, and it goes back and back on a long trail and this
03bda0d33efb2da41c117c139279c1811d297637468c404d487c1d678e974b02 transaction is where the issue began because the funds send from here consists of 500 small UTXOs which made the transaction size to be around 75KB and why you have to spend 0.25
BTC to do CPFP.