I don't see why this is downvoted. Domains assign reputation to mail instead of the source IP, and it's fairly obvious that just buying a new domain and spammin

I don't see why this is downvoted. Domains assign reputation to mail instead of the source IP, and it's fairly obvious that just buying a new domain and spamming from it would tank that domain's reputation for quite a while, even with proper spf/dkim and dmarc p=reject. If all of these are set up, you won't have issues sending from bad shared IPs like the default SES ones.