I think it's not me who's confusing here. You're comparing replicating appearance with replicating appearance, which by no means is the same thing as producing the exact ability as the original—regardless of whether it's a devil's fruit ability or not. VP uses the linage factor to replicate all kinds of abilities, so the process is the same for both, and he never managed to create something as good as the original.
Bruh, you're comparing the skills of children, to thier adult counterparts with decades of experience, as a means to justify them not being as strong as the originals.
Furthermore, you're comparing an artificial laser, to a Devil Fruit.
On the flip side, Vegapunk perfectly replicated Kaido's Devil Fruit powers. It was only deemed a failure because the color of the dragon was different.
The fact that all the Seraphims look exactly alike thier adult counterparts is indication that the DNA replication was a complete success. Because they are not as strong as their older, more experienced counterparts is not an indication that they are watered down versions.
You can only make that assessment once they get older, and have a real basis for comparison. But I guarantee you, Child Mihawk and child Kuma would not be giving Luffy, Zoro, Lucci, and Kaku even the slighted bit of challenge, like the Seraphim are.
And the final nail in the coffin, is that Zoro, who already fought King, can't damage the Seraphims. He's the one telling everyone else that it's practically impossible to hurt these things unless they turn thier flames off.
He's gives no indication that the defense they possess is any less effective than King's. In fact he does the exact opposite, by saying with the flames on they are practically invincible.