The depreciation method my accountant chose is cutting my passive losses in half compared to what the other one projected

The misconception worth naming: the gap between the two projections is not one accountant being wrong. It is two different methods, both defensible, with genuinely different outcomes depending on your situation.

The question that decides whether the cost segregation number is worth chasing is whether you can actually use the passive losses it generates. If your adjusted gross income is above $150,000 and you are not a real estate professional, most of that accelerated loss suspends until sale regardless of how the study is structured, which makes the present-value math much thinner on a small residential property.

What is the depreciation basis each accountant started from, and do you have other passive income to absorb the losses in the near term?

The $4,800 gap makes sense once you see where it came from, and your framing of it is accurate.

Straight-line depreciation means you divide the building's value by 27.5 and take equal slices every year. Cost segregation is an analysis that says "some parts of this building wear out faster than the structure itself, so let's put those parts on shorter schedules." Carpet, certain fixtures, and land improvements like parking surfaces are examples. Shorter schedule plus bonus depreciation (a rule that lets you take a large chunk of a short-lived asset's value in year one) produces a much bigger year-one deduction.

The thing worth sitting with is your point about total depreciation. You do not get more depreciation over the life of the property. You get the same amount sooner. The value is the time value of money: a $10,000 deduction this year is worth more than $10,000 spread across seven years, because you can use that tax saving now. Whether that present-value benefit covers the study cost depends on your marginal tax rate, whether you can actually use the passive losses (you need passive income or a qualifying exception to absorb them), and how long you plan to hold the building.

On the credentials question: the IRS has been consistent that studies done without a qualified engineer carry more audit risk. If the second accountant estimated component values from a spreadsheet rather than commissioning an engineering-based study, the numbers may not hold up.

A tax professional with real estate experience, specifically a CPA or enrolled agent who works with investors, is the right person to run the payback math for your specific situation. That question is outside what I can answer here.

What does your passive income picture look like across your other properties? That changes whether the timing advantage is real or theoretical for you.