Leviathin and Samson's rivalry is between each other, as Parasites. Sure Eliza is familiar with the two of them, but I figured Sekhmet would be the one giving the trash talk.
If it weren't for Eliza talking like a normal person while Sekhmet shouts nihilistic gibberish I'd be certain they were the same person. It doesn't help that they haven't ever spoken to EACH OTHER yet, like Sam/Fil and Lev/Squig do during combat, but it seems unlikely that they won't talk to one another in Eliza's story mode.
But perhaps Eliza is meant to represent the apex of the Parasite/host relationship. The team liked topint out how Samson and Filia aren't completely in sync and he pushes and pulls her around, whilst Squigly and Lev have a nice dynamic and work together like a pair of dance partners.
One last lore musing: Leviathin was present when Eliza & Sekhmet fought Samson & Delilah, but who was his host at the time?