I challenged about 8 years ago and won. It took about a year. I was dealing with SDAT assessors who seemed clueless. Eventually, I got a hearing and won. I had stacks of evidence, including data on many comps.

It's a frustrating process. Be diligent.

The assessors are completely overwhelmed. They have too many houses to assess, and their evaluations make little sense. After studying this for a while, I concluded that a major problem is the number of homes that are assessed for way under market value. (Sounds like OP is seeing this with their neighbors, which is what I saw too). I think assessors under assess because they know the city's tax rate is so high. Some of us are unlucky, like me and OP. But most homeowners are actually pretty lucky in this regard, i.e. their assessments don't increase to current market values, especially if the sales occurred years before.

If the assessments were accurate and matched current market values, our property tax rate could be slashed with no reduction in total tax revenue.