This is an easy one. Your program's ranking certainly can have an effect, but it doesn't necessarily spell INSTANT JOB. It also doesn't necessarily spell INSTANT REJECT. It all depends on the post-PhD job you're applying for. The more closely and tangibly your skillsets and experience are a fit for the job you're applying for,
Is a PhD on a relevant subject as valuable as spending the same time gaining work experience in the same field?
This depends. How easily can you get relevant experience in your PhD vs in the workplace? PhD research typically is centered on deep investigation of a specific niche, and depending on where you are, that may be more easily accomplished in either scenario. More relevant to your question is what do you want to do