Thinking about it, it's probably easier to spotlight 5 in a movie than 6. Remember how underserved some of the Manes were in the last one?
I think that's just an inherent problem with trying to make a FiM movie. So much of the "bread and butter" of screenwriting just doesn't work when you have seven main characters that can't undergo any kind of change over the course of a movie. Five is an objectively better number, but the more important thing is that these characters are built from the ground up to be used in a movie. @Background Pony #EF5D
That movie also had the problem that they tried to shove characters and locations for a whole movie trilogy into a single movie.
Not really. The original Star Wars had Leia's Ship, The Tatooine Wastes, Mos Eisley, The Millennium Falcon, the interior of The Death Star, and the vicinity of The Rebel Base. The Pony Movie had Canterlot, Kludgetown, The Pirate Ship, Mount Aris, and Seaquestria.
If we start with R2D2 and C-3PO, then a total of five characters join the party throughout the course of the film. There's also a similar amount of named villains. Star Wars is two hours long, and The Pony Movie is an hour and forty minutes. I would say The Pony Movie is about as dense as Star Wars in terms of characters and locations. The Pony Movie just feels a bit more cluttered in terms of characters because we follow seven leads from start to finish.