No one here knows how many characters he planned for because no one has seen his "script." You're speculating that he planned for 79+ characters when for all we know, he could be adding characters "on a dime." And my question is, why not take the one-and-done and replace them with more development time applied to the main LIs. Also, Here is a statement from L&P three years ago from one of his members about the characters.
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He even knew then he had too many characters and plots, which is a general statement from the first sentence in his answer.
I have to look for it again, but I remember something from L&P saying that the dental scene was more of a realism scene to show the reader that she has a daily life, and it most likely won't be used again, sort of like Dylan's ninja training scene with his sensei. IMO, this was a scene that I could have done without seeing the dental office. I didn't have any breakthrough connections or moments with her getting her teeth polished.
Can the reader still connect and care for Sophia with fewer characters and scenes? IMO, you can. Does less give more? If the story is written well, then yes. He could have the same impact with Sophia with a handful of characters like Dylan, Ellie, Patricia, Alyssa, Zac, Julie, Nathalie, Liam, Carl, Neil, Amber, Andy, Cathy, Christine, Aiden, and maybe a couple more and be very effective at telling his story. More scenes don't always equal better.