When you break fast and move things, Docker is invaluable. I have more than one product and something like Docker makes it tractable for a single person to support.
Still, I run it all on one server using Docker so there is a medium :-)
How often are you spinning up new servers? In one to two hours, I can configure a production ready Debian server from base install with firewall rules, correct network interfaces, cron jobs, all dependencies and tooling, monitoring, Postgres, and my application server (either C epoll passed or Spring Boot) sitting behind an nginx proxy. I would consider myself neither a Sysadmin nor particularly fast at configuring Linux.
One to two hours per project multiplied by potentially one or two QA/UAT environments, and this is a tiny blip in the total time spent developing a solution. I think it would take me a few years before I paid back the debt of learning docker/kubernetes for it to actually start saving me time as a freelancer (or if multitenancy suddenly becomes out of the question).
At my job I regularly spin up ~1000 servers to test some workloads or do some data processing. Would be a pain to do that manually, and spinning up 1000 servers isn't significantly more expensive than 100 or 10 but it is significantly faster.
Still, I run it all on one server using Docker so there is a medium :-)