It has happened multiple times in our company that people not familiar with this plugin will add a single container and then forget to define a container step.

I believe it would be sensible to default to the users container instead of the jnlp container if there is no container step specified, especially when there is only one user container specified.
This will allow them to not have to worry about the internals of how the plugin works, specifically that a jnlp container is added.

It is especially confusing when the first example does not mention the container step

podTemplate(label: 'mypod') {
    node('mypod') {
        stage('Run shell') {
            sh 'echo hello world'
        }
    }
}

P.S This seems to be a duplicate of JENKINS-41109 but that was closed without a fix 8 months ago?