Plenty in the Trans. tier, imo. At that point, "weakest" becomes a bit subjective. WBH was probably safely above high herald, but the top feats for guys like Superman, Surfer, and Thor are also well beyond anything traditionally associated with the high herald level. So then it becomes an exercise in determining which feats count for more, and which interpretation(s) you give validity to.
Skyfather is a safe guess, but I think it also undersells several in the Trans. tier.
Point being, there aren't objective, irrefutable answers to questions like the OP's.
Standard Hulk showings are far above Herald tier as well and we know that World Breaker is tiers above him. This isn't a ft war this surrounds power level. Power level wise, World Breaker were stomping beings that was above Top tier without even trying.
He's got limited showings, I think you're overselling him, and Surfer and Thor have abstract-busting attacks in their canon. I'm not saying they're above WBH. I'm saying there's a lot of interpretation and subjectivity involved. Nothing WBH did trumps what a lot of Trans. characters accomplished.
Your Skyfather post is the highest opinion in the thread so far. I said that several in the Trans. tier could. So, let's stop for a second and realize that I'm saying that some of the characters in the tier immediately below Odin could beat him for a majority. We're talking about small degrees, not about massive differences of opinion.
They already did a comparison between Surfer and Hulk before going World Breaker and Hulk stomped a being that was said and shown as being comparable to Surfer.
World Breaker being above Herald tier was an average showing for him. Using High showings for standard Hulk would make World Breaker a pointless character. The point of all of this is,World Breaker was leagues above Herald tier. Hell, they even tried to sell to us that WWH was above Herald tier as well (him killing beings that were leagues above Hercules and his showing against the Avengers when he basically called them fodder (including Thor) and to make room for someone who's challenging, his son). I can see where you are going with the high showing argument but it was obviously more to that than just picking and choosing of fts.
I actually agree with a lot of this. But I think you may be getting hung up on the tiers as literal ladder steps of power. I'd classify a lot of Trans. characters as "leagues above herald tier" just like you do with WBH. There are several that I think would run through tons of high heralds with ease, including the "Big 3" of Supes/Thor/Surfer.
So yes, it's one step above HH according to our arbitrary KMC distinctions. But the actual gap in power can be considerable between any herald and those among the most powerful of Trans. And I think several Trans. have the feats to match him.