If I may be blunt, if we're treating Smash Speculation in the same manner as we would treat science... then the entire "new worlds" theory (at least in August 2020) is bad science.
Science at its core is a dialectical process that follows a somewhat specific pattern. First, a phenomenon is observed. Next, someone presents a theory that purports to both explain why this phenomenon is occurring and what phenomenon will occur next. The theory largely stands as fact, until someone notes a phenomenon that either contradicts the proposed mechanics of the theory's explanation or could not have been predicted by the theory. At this point, the old theory is abandoned and a new one takes its place that can better account for new phenomena. Rinse and repeat ad nauseam.
What isn't done in science is the alteration of semantic definitions that make up the theory's terms. Take the discovery of heliocentrism. For awhile, geocentrism (the view that the Earth was the centre of the world) was widely accepted, because it explained phenomena like the sun rises and falling throughout the day. However, as the methods and tools available to study space advanced, certain phenomena that couldn't be explained by geocentrism emerged. To account for this, the theory of heliocentrism (the sun as the centre of the universe) was proposed. This theory accounted for these new phenomena that could no longer be explained by geocentrism using a new explanation and a new method of prediction.
While it was a very controversial change that many adapted to at different paces, it was the right move. It was time to take out the old and bring in the new. Even if the heliocentric view of the universe is largely being phased out by recent scientists, it was a valuable stepping stone to where we got to today. What would have definitely been the wrong move would have been redefining the meaning of "centre of the universe" to artificially extend the life of geocentrism. People can reasonably disagree about something what exactly "the centre of the universe" really means, but it would have been much less efficient and effective at advancing our understanding of space relative to developing a new theory from the ground up.
Now, the "new worlds" theory made a lot of sense when Sakurai first used the term in the Banjo presentation. The previous four characters (
,
,
, and
) were all from series and games that had no previous representation in Smash Bros., so the theory would have been somewhat effectively at zeroing in on their inclusions when applied retroactively. Similarly, the entire theory had a relative strong causal explanation behind it: Sakurai is well aware that Ultimate is likely going to be the peak of the series both in size and fan service, so he's trying to see just how much further he can extend these elements through DLC. Even the first new phenomenon after the "new worlds" theory, the inclusion of
, seemed to suggest some predictive power. While Byleth was a series with content previously in Smash, he was from an entry in that series that had no representation in Smash. Plus, I do remember people who supported the theory saying that it would make sense for a Three Houses character to join Smash, so it wasn't logically inconsistent then.
However, I really see no way to square the circle around
. First off, there's no way to have the new worlds theory predict an ARMS character, seeing how the series already had five spirits and two Mii costumes in the base game, thereby excluding it from a future DLC pack by the logic of the new worlds theory. Similarly, Min Min doesn't fit with the theory's main causal explanation behind character choices. How does the inclusion of a character that was already in Ultimate as a spirit accomplish Sakurai's goal of expanding the crossover? It's still new content, but it retreads a game and series that was already represented in the base game.
Admittedly, this post kind spiralled out of control and mutated into a massive essay, but my key point is this.
New worlds theory made sense in the past and no one can really fault folks for believing it back then. However, in the face of contradictory evidence, it's time to let it rest. If we want to keep to a consistent standard of logic and science, we aren't benefitting speculation by constantly moving goalposts to try and keep the new worlds theory relevant.