u/Moravian_Reenactor

First things first, let's specify what is canon in the Hellaverse and what's not, because people love to use outside lore and headcanons to glaze Lucifer. "He is the first and brightest angel", "He was God's favorite and his right hand", "He was an Archangel", none of that is canon in the Hellaverse. Lucifer was just another Seraphim, he wasn't even popular among the angels. Everyone saw him as a troublemaker and he was an outcast.

And yes, Lucifer is a Seraphim. He is not some ultra powerful angel that used to rank above Sera, he was and is a Seraphim. Aside from the official Italian dub saying he has "Seraphim power", Viv's August 2024 Patreon Q&A outright confirmed it:

"Were Lucifer, Sera and Emily created by the Six Elders of Seraphim?"

"Technically, Seraphim are the top. There's technically one class above them, but I cannot say what that is. But they are very close to the top, so they were not created by another class."

In her response Viv grouped up Lucifer, Sera and Emily under the term "Seraphim", so he is a Seraphim. Now that we got the misinformation out of the way, let's explain why Lucifer isn't stronger than Sera. I'll have a brief analysis here, but anyone interested in a more thorough version can check the images of the post.

Without going all out, Sera was a major contributor to the creation of Heaven's shield, and she likely provided more energy than any other angel there. She used her normal form for the majority of the ritual and only powered up with her multi-eyed one (which made her beam 2x-4x larger) for a single second. Aside from barely even using her second form, she didn't use her true/holy form at all, nor did she show any signs of fatigue or strain, like Emily did when creating the Egg Bois or Lucifer when he was powering the cannon.

This shield held the cannon's beam back for 18 seconds and absorbed most of its energy, considering that the beam didn't even reach the city a few hundred meters behind the Pearly Gates. That beam should be equal to Lucifer's max power output, since the cannon was taking enough energy from him to cause him strain and pain. All of the above together suggest that at full power, Sera should be comparable to Lucifer, or at the very least to a considerable percentage of his power.

Narratively, she is said to be the highest Seraphim and the recent Hazbin Hotel Bar Book outright confirmed she leads the Seraphim. That puts her above Lucifer in the hierarchy, and usually there is some correlation between power and rank in the Hellaverse.

The conclusion is that Lucifer glazers need to separate canon from headcanon and accept that their goat isn't standing comfortably at the top of the verse or anything like that. Sera is more than capable of matching him in terms of power, and the Speaker is most likely stronger than him.