oh wow, we have some lore under this text lore: shattered thunder is the pure disruption of timelines, as thunder technically never had the ability to teleport to other universes. the one you always saw in collabs was once thunder, but sometime in the past became the shattered version.
and then we just have S-A!User, who is literally a stressed out version of Classic User who puts people before him in terms of things like safety and well-being.