Gematsu leaker definitely had legitimate information, but it's extremely unlikely that it is all the newcomers we have left. First, the leaker never claimed to have the entire roster, and as I pointed out before, all the revealed newcomers and those implicated in the leak are characters from recent/revived franchises, being used to promote their games. It looks like that pre-release newcomers this time are being those they can milk the exposure from to sell some extra games and drive up hype for other series, while those with nothing to promote are being kept as secret unlockables. It also goes in line with the thought that the Gematsu leaker is someone involved in marketing, who would have the knowledge of which characters they're planning to reveal, while not knowing those that are being kept back with no plans for a pre-release reveal.
Also look back to my previous post on how a 50-52 roster looks very likely, with 3-5 more unknown newcomers. As such, don't expect Gematsu to be it (and in the worst case scenario that it is, it means we'll be getting DLC anyway).