The article quotes the CEO saying yield is comparable:

>TSMC’s new Arizona plant is already comparable with those in Taiwan when it comes to the measure of yield — the amount of good chips a production run produces per batch — Su told the audience at the forum.

The overhead cost of a fab is fixed. So hard to understand why that would have such a wide variance. It may be true that the facility hasn’t been fully amortized so in principle it’s more expensive to make chips there. I can understand it being more expensive for many reasons. However I wouldn’t expect the cost difference to have a large variance. 5-20% is a very large range if the yields are comparable.