Kakoune has a client/server mode so that the client instances can talk to the same server. This way unsaved changes to a buffer are visible across instances + all the registers etc are shared.

Helix doesn't have that functionality. Kakoune also doesn't have splits at all where as Helix does, so the design philosophy is different between the editors.

Personally, I would prefer if tabs were first class citizens in the editor, but would make do with scuffed tabs if there was a server/client model implemented.