I don't know which arranger but it could very well be a Solton since AJ wrote it in 2002-3. Yep, it does not sound like an arranger, good job. And your work here is very good, a very good video. I think the weak spot is the sung vocal audio quality. MLK was one of the greatest speakers ever born and you've captured his magic with the various excerpts, but to me, the weak spot is in clearly hearing the sung vocal. It's a song, so, I think you should re-record the song or master it again so that the sung vocal is clearer. And also highlight the hook in a couple of spots, so that it is clearly heard. Maybe even remove all music around the sung hook once or twice to hit home the powerful message... "I have been to the mountain" or whatever it is. However, take all of that from someone who has high-frequency hearing loss.
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Bill