To be more specific, let's say Sakurai had this as his shortlist:
Original Characters
- Inkling
- Ridley
- Simon
- King K. Rool
- Incineroar
- Isaac
- Shadow
- Banjo
- Sora
- Geno
- Piranha Plant
Echo Fighters
- Daisy
- Richter
- Chrom
- Dark Samus
- Isabelle
- Ken
During development, Sakurai realises Isabelle are becoming a little
too different from Villager, and so he decides to break her off as a character to be her own thing; however, this causes a shift in focus.
At some point later in development, Sakurai realises that Isaac, Shadow, Banjo, Sora and Geno are not going to be done in time for release (maybe the Veterans were more difficult than Sakurai thought they'd be, or maybe he initially expected the game to release July 2019 and the date got pulled forward and those characters were lower priority). So they stop/slow production on them for the time being, Isaac and Shadow are repurposed back into Assist Trophies so that they are
at least in the game (seriously, people would complain if they weren't, especially Shadow, trust me).
However, this also gives them five characters to work on for DLC. As for Piranha Plant, I'm sure he's not...
that difficult to produce, relatively speaking. XD
Now, I don't want to hear "that's
such a stretch" or "that's insane/straw-grasping" or "but [leaker] said this", because I am
100% aware that I am probably wrong.