Where exactly does this originate from? I have seen this sentiment, or something similar, many times in the past few days but never heard how people came up with this idea. Is it just a nameless rumor or was there a verifiable source that suggested it might be the case?
There are a few things that go into it, and I should probably reword my previous comment to reflect that. We don't
know anything for a fact, but here goes nothing!
We recently learned that Steve was in the works for a few years, and it's plausible to suggest that Steve was handled alongside Banjo-Kazooie. Byleth was obviously chosen before Three Houses released. Min-Min (or at least an ARMS character) missed the base roster, and we didn't get an ARMS stage or music selection.
We also know that Nintendo made certain decisions, that Cloud was difficult to retain (from insiders iirc), etc. With that in mind, if you piece a few things together, it seems to suggest a few things.
1) Joker and Terry are Sakurai picks. He loved the art style of Persona 5 and he grew up playing Fatal Fury.
2) Sakurai was essentially told to add a Three Houses character, and ARMS was a special request from Nintendo. This suggests these characters are "corporate" picks, being different from the picks Sakurai made.
3) Considering the situation with Cloud (likely coming down to money issues vs. Nintendo wanting Everyone is Here), I find it plausible that the negotiations took the turn toward..."you scratch my back, I scratch yours", and resulted in Cloud in base roster, with Sephiroth pushed to DLC. While this is speculation on my part, I THOUGHT I heard that somebody, an insider, mentioned something similarly.
This could also be a bundle of nothing, but I frankly feel that where there's smoke, there's probably fire. It seems wholly plausible that picks for both passes were decided around the same time, and that Pass 2 was planned sooner than we think. At least, considering we have a three-peat going with companies from last pass (Nintendo, Microsoft, Square Enix), it seems plausible that they were negotiated for at the same time.
It ALSO would explain why certain Mii costumes didn't come back during the first Fighters Pass. There's really only two ways it would have panned out- either they selected costumes conveniently from companies we would double dip in...OR...it was planned this way from the start, especially considering we didn't get popular choices like Geno, Lloyd, and Monster Hunter costumes.
It may appear just to be me theorycrafting, and it totally might be! But I certainly think there's a case to be made for it.