12 factor apps sacrifice performance and simplicity of your environment for scalability. Unless you are guaranteed to start with a worldwide audience its complete overkill. A better solution is to write your application with the rules in mind with the goal of making it easy to transition to a 12 factor style app when its needed. Scale up then scale out will result in the best performance for your users.
The 12 factors are mostly common sense that apply in pretty much any situation - they help with fancy deployments but also with single servers on DO or even on-Prem servers.
The thinking on efficiency vs scalability is largely influenced by the US tech company meta where founders give up equity so they don't have to worry about profitability for a very long time.
In that case, it is preferred to burn piles of cash on AWS instead of potentially needing to sacrifice revenue because you can't scale quickly enough.
An architecture that is not scalable is considered a failure whereas one that is complex and inefficient is much more tolerated (as long as it can scale out) ... at least until the funding dries up or Wall Street activists get involved.
I think the important issue when first starting a project is to create a "12 Factor App" so that if and when you create a Docker image and/or run the application in Kubernetes, you don't have to rewrite the entire application. Most of the tools I write run on the CLI but I am in fact a fan of Kubernetes for services, message processing and certain batch jobs simply because I don't have to manage their life-cycles.