You’re right @Kevin, my apologies, it helps to use an email subdomain for marketing emails, especially if you run the risk of lowering your main domain reputation with the marketing content.
I was rather looking at the simpler solution as subdomains on the same DO droplet with the same maybe poor reputation IP doesn’t seem to help much (as emails still end up in spam). Rather go through the cost of having a dedicated IP address and clean its reputation as I think that part is more important than the subdomain extra protection.