Are you looking for a data entry clerk, or someone who can work with clients and spot what documents are needed, not just process those that are provided?  Interviews are generally the least useful method to identify the best potential employees, so of course that's the system most organizations use.    If it's a public-facing job, though, it can be part of the process.

Your hiring assumption is that someone may be smart enough to pass the CPA or EA exam, but not smart enough to work for you?  And you still have competition for people who will go along with that attitude?  AI must have eliminated more jobs already, than we suspect.  

An applicant could have years of experience preparing hundreds of returns with one brand of software, but still struggle with Intuit quirks.  Or have experience with ProSeries, but also have dyslexia that no one has yet spotted.  The software doesn't tell you that the number is 736928, not 729638.  I did a Google search for dyslexia testing, and there are professionals who do that for a fee.  

Hiring employees is difficult.  My technique has always been, to rely on luck.