Cloud resources should be a commodity. Providers should offer compute resources, persistent storage, load balancers, and MAYBE a small handful of other services.
The way Digital Ocean succeeds against AWS is by aligning itself with this idea, and competing on specialization. Forget competing with lambda; let me run my own serverless application. Don't worry about IAM; let me configure LDAP. Don't waste developer hours on service-ifying the latest NoSQL storage trend; write high-quality tutorials explaining how users can do it themselves.
And most importantly, continue to invest into open source and community resources. There are developers willing to fight the good fight against proprietary walled gardens like AWS/GCP/Azure, but it has to get easier. Configuring HA postgres is harder than paying for RDS. Paying for GKE is more feature complete than using rancher or kubeadm to make my own kubernetes cluster. This friction is an existential threat when Azure can make my problems go away for cash.
I don't know if Digital Ocean can succeed against the big cloud providers, but if they do it won't be because they made a better platform; it'll be by playing a totally different game.