There are no extended instrumental parts or solos on Bridge. And string arrangements may be a difficult thing for inexperienced or not properly educated musicians, but for a pop-rock song some times it is considered such a simplistic thing that usually they don't even demand an arranger credit, if money is good. And many big studios used to have such arrangers as part of the household services. Of course other times the composer gets a composition credit on the song, because his ideas infiltrate the composition (like Ron Gessin on Atom heart mother etc. ) And I can only imagine what would Marvin Gaye's What's going on would have sounded like without the input of all these great musicians and arrangers. The first test - singles have the original orchestration that although they are away from the traditional Motown sound, are still a long way to go from the masterpieces versions that finally appeared on the finished album .
And these appeared commercially!