I mean, its also essentially tax free money as you get a ~.50$ tax relief/mile driven, so IMO with all the costs you probably are equivalent or possibly better than a 21/hour job.
A $21/hr tax-free job minus driving costs is still equivalent to a $15/hr job. It's definitely not equivalent to a $21/hr job riding around in someone else's ambulance burning someone else's gas. And from what I'm seeing, residents make ~$60k/yr. That job is also a stepping stone to a much more lucrative profession.
That’s only if you believe in the fairy tale that Social Security and Medicare taxes (close to 15% including the employer’s side) go into a separate account and that those taxes don’t go into the same bucket as regular tax revenues.