I see what you’re trying to say, but your generalized assertion about the talent is faulty. I don’t think you can say they have more talent than any of the other top groups. Top three or four horn lines have similar talent level. Top six drum lines, crazy talent. Top three or four color guards, same.
The difference is finding a specific performer profile, including visual capabilities. It’s not just enough to be able to play or spin at the highest level. You really have to be able to move, and “perform”. This is true at a number of other top groups at specific captions, but there’s nobody that really has that top to bottom like BD. The gap is closing though.
There is plenty of talent to go around. BD still wins because they put together the best programs most years, and manage to get the most out of their kids, at the right time. I can think of a couple of recent times they closed the deal on finals night with a peak performance…2007, 2015, 2019 come to mind. They have also been bested by some amazing programs and corps…2008, 2013, 2016, 2018.
As for migration from other top groups? Yeah, it happens but the number is not huge. There are also extremely talented individuals that do not make BD that go onto the other top groups. A particular winky trumpet player comes to mind. Lots of mad talent that audition at BD, then move on to, and are a great fit at another top contender. So I think the raw talent is comparable, but maybe BD just does a better job screening for their needs.