I think you're misunderstanding the challenge. Teaching first year students doesn't require Ph.D.-level knowledge, but it requires more teaching experience and

I think you're misunderstanding the challenge. Teaching first year students doesn't require Ph.D.-level knowledge, but it requires more teaching experience and skills than teaching later levels: The classes are larger; the students are less experienced at learning on their own; the students are new to the environment and less familiar with how to navigate it. Large classes of novices are particularly sensitive to logistical and teaching errors. You make a question on a homework or exam a bit confusing, you have 400 students utterly perplexed who may not have the domain expertise to know it's the question that's broken. At Carnegie Mellon, our teaching-track faculty generally own the large intro classes for this reason. They're the best we have at the process of teaching & education. It's the exact opposite of a side job. You want people who are deeply expert and passionate about teaching so that you don't completely botch the job, because the opportunities to botch it are huge.