There’s reason to believe that Soldier Boy and Stormfront could be competing for the number one superkiller spot, but without further evidence it’s a bit tenuous.
Remember Termite (Brett Geddes), the shrunken hero who finds himself in another man’s body in a totally unexpected way in the Season 3 premiere? Yes, he’s one of the victims of the “Hirogasm,” but not at the hands of Soldier Boy.
Not long after Soldier Boy unleashes a deadly power-nullifying attack on Hirogasm, we see a shrunken Termite injured and crying out for help, his “help” appears in the form of Homelander’s boot, crushing and killing him.
When talking to Maeve, I think Homelander may have counted Termite among the superheroes killed by Soldier Boy, not just to deflect blame from him, but because of Homelander’s warped thinking (i.e. “without Soldier Boy I wouldn’t be there, so it’s Soldier Boy’s fault, not mine”).
If that were to happen, Soldier Boy’s number of superkillers would drop to eight, matching Stormfront’s.
But until such a thing is confirmed, Soldier Boy remains superkiller No. 1. Yay, Soldier Boy.