You have a salient point in regards to mask vs identtiy being an abitrary distinction and I agree it's definitely a spectrum to an extent, but thaat's nothing to do with the majority of the people on those subreddits and tiktok circles. They will literally fake seizures or passing out to indicate when they change between alters, or insist that they have literal fictional(often anime) characters as part of their "systems", and do these delusional showcase videos where they will rapidly shift between all of their "alters" on video, changing their facial expressions and posture to signify that they're a different one.