Show me any DIRECT statement saying that Enny is STRONGER than Serena. The official translation just uses the word FRIGHTENING. By definition something frightening is something that makes you feel fear, which in context implies that they have high power but DOES NOT directly ranks them as he could just be talking about the nature of their abilities, otherwise he would have just said ''you think i'm powerful? they are much more'' but it wasn't what he said. So no, not a single statement makes Enny win
You can also check the japanese word used
Yabee which is a slang for yabai, and these words can mean: dangerous, terrible, extreme, etc, so nothing that correlates to powerful or strong
Didn't knew you know Mashima personally to know what he would write, did you have Mashima number with you?

without Mashima words this is just headcanon and i'm discussing what actually happened and the reality that
there is no single statement putting Enny or Luso above Serena.
Feats: Serena>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Enny
Statements: GS was said to be stronger than Laxus at some point and even Gildarts praised his full power alive version as an opponent for himself while signarios can't leech GS feats just being more frightening than him so by statements GS>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>Signarios