Good mechanics are a given at that level of performance. If you can play like Yo-Yo Ma with bad mechanics, more power to you, an orchestra is not going to care.
If you're hiring for some mid-level orchestra, bad mechanics on a sufficiently-skilled player might be enticing. And as you say, bad mechanics among top performers are basically nonexistent.
Perhaps a better example would be a teacher identifying the most promising school/college-age musicians?