Off the scale
One of these two was never ranked, so this cannot move a ranking it is not in.
Nothing moves, because one of the two has no position to defend. The killer is listed and argued here but deliberately unranked, and an entity that reaches this universe by wearing someone else cannot be placed on a ladder that measures what things do under their own name. What remains is a claim about a branch of the future: one timeline, no depiction, `stated` and nothing better. The books also hold that this victim has never been written anywhere near his limit, which makes the episode evidence about a possibility rather than a result.
The One Below All killed Franklin Richards in The Immortal Hulk (2019).stated
in a far-future timeline, and recounted rather than depicted
Named as the inverse of the One Above All, dwelling at the base of the Below-Place.
In the far future it kills Franklin Richards, Galactus and Mister Immortal, until nothing else is left alive. — 2019
Possesses the Leader, who has stolen Banner's body, and is fought directly when it manifests.
The other end of the same being. It lives at the bottom of the Below-Place, it wants everything that exists to stop, and its route into this universe is the Hulk: every gamma death goes through its door and comes back wrong. It is up here rather than ranked because it almost never acts as itself — it works by possession. In one far-future timeline it wore the Hulk as the Breaker of Worlds and killed Franklin Richards, then Galactus, then everything else, because what it wants is to be alone.
The pocket world the apparently dead heroes have been living in is revealed as his creation.
The mature Franklin restores and empowers Galactus, who becomes his herald. — 2012
When Onslaught apparently killed most of Earth's heroes, Franklin had already built them a working universe to be alive in, and it ran for a year of publishing before anyone worked out where they were. He was a child. The books are consistent that this is nowhere near his ceiling.
One death in one work. It is the only place the record puts these two in the same room, and it is evidence about that meeting and nothing wider — not a general matchup, not a rematch, and not a ranking of its own. The ladder above it is argued from everything either of them has been shown doing; this page is argued from one citation. Where the two disagree, the disagreement is the point, and it stays visible rather than being resolved by whichever of them happens to be on this page.
Both entries carry their full receipts on the Marvel ranking — 5 citations between them.