He might have his strengths as an OC, sure. But our biggest problems on offense are the line and the running game, and Harrell brings nothing to the table that would suggest that he'd be an improvement in those areas.
That said, I think people are reading a little too much into the rumors around Harrell. It's clear that he was an early candidate, and there was some mutual interest. But I think the 'early' part of that is being overlooked a bit too much. If Frost were ready to hire him just based on those early impressions, we wouldn't be sitting here waiting a month to hear who our next OC will be.