All singers have "vocal problems". If you name a singer, someone can pick them apart in some set of categories. Every singer is going to be "flawed" in some way. The singers each approximate what is on the score based upon their genetics, history, training, technique, vocal health, physical health, emotional state, acting ability, experience, and appearance. (I do not presume this list is complete.) Given that each of those values are not yes-no, but are quite deep in ranges of values, we are talking about billions and billions (yeah, I know) of combinations of values that determine the state a singer can be in for a performance. Every one of those values is an adjustment they try to make to perform to the best of their ability.For example, genetics can be compensated for (somewhat) with history (how you've cared for the voice in the past), training (the luck of getting a teacher who can guide you to use the genetics), and technique (what you've learned to do and not do with the voice to achieve the effect). So, each "column" is adjustable. The singer's job is to keep the "bottom line" of the columns to a level that is satisfying to the audience.
Just as there is no amount of tension you can apply to a string to make it hang in a perfect horizontal line, there is no value high enough on any of those categories to compensate for any one of the others when it is low. So, every time a singer gets on stage, one or more of those values will work to sabotage the performance. You then have to add how each of us "weights" the values of each column. To someone who does not care about acting, no matter how great an actress someone is, it does not make a difference. To someone who wants great acting, note-accuracy and intonation are less noticeable. And if the audience is just "not with" a singer, there is no level of perfection that will make them like her. The bottom line on my "spreadsheet" for Ms. Voigt's performance having watched it twice (in HD) is that she delivered the goods as well as anyone else could have taking all "columns" into account. I am sorry her directions were limited to those designed for Ms. Eaglen. But it was thrilling, radiant, glorious, and satisfying to me.
Interestingly, I read James' analysis while sitting in the theater during the intermission of the encore presentation. And much of what he said, I could hear when I listened for it. It didn't make a difference. We can point out everything that was wrong with that performance and other performances. But it doesn't prevent my enjoyment of it. I hope I continue to be able to find something to enjoy in a performance that makes giving my attention to it worthwhile.