Based on the mix here, I’m not sure there would be a lot of room for the addition of a bunch of percussion or a guitarist. Those strings are taking up a LOT of sonic space, and the arrangement uses them up front and loud and proud! Which is very much the goal, I imagine. I’m not sure how much you’d have to subtract from that great arrangement to leave room for a couple of additional players… probably so much it wouldn’t have the same impact.
This is the genius of not throwing the kitchen sink at a song..! The smaller rhythm section makes the strings shine, IMHO.
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An arranger is just a tool. What matters is what you build with it..!