What prompted your job change that was a step down in responsibilities? Were you unemployed and took what you could find or did you make the change purposely?

I would practice answering the interview question "Why did you leave your last position?" It's common. I would suggest a simple non detailed answer like "the position I was hired to fill changed shortly after I began working for XYZ CO. My skill set wasn't the best fit for the modified position." From what you said, that's all true. It's also understandable that things just didn't fit right and lead to your job search. If there's followup such as what changed? The job responsibilities I expected were redefined and no longer aligned with my experience and strongest skills" then change to asking a question specific to the job as it relates to your skills. Something like what skills are critical to success here at 123 inc??

It sounds too like your last employer used a "no fault" reason for ending your employment. Regardless of what you think the reasons were or what they were thinking... the official reason is that your skills no longer matched the needs of your employer. You still have a dynamic skill set that has value to an employer.

I "officially" left my previous employer because my job relocated out of state and relocation wasn't best for my family at that time, And that's what I said in interviews. Reality was I hated the idiot I worked for and when the company moved 20 miles over the state line my commute in a different direction increased from 21 miles to 33 miles. But because the office moved over 50 miles and out of state, no one ever questioned me further.