Just in terms of the humor in Pitch Perfect 3, it’s way funnier to see Beca spurn Theo’s advances over and over again than it would have been to see her cutely melt into his arms at the end of the movie.
Having seen the movie, I personally feel this was the best call for the script.
Per Anna Kendrick, getting jiggy with the guy who was willing to give her a big break based on her talent and not just her looks would have been sending a message to the audience the actress really didn’t want to send.
It even leads to a really funny gag during the end, where Theo and Beca see another couple making out and he tries to lean in, only to have her brightly turn him down so they can discuss her being a handful to work with.