The Issue with your statement is you claim Elfman fodderized Leo as though Mirajane wasn't also apart of the fight despite the fact we see both of them attacking Lucy and Leo. So your statement instead should read Elfman+Mirajane fodderized Lucy's spirits as Elfman didn't do it alone.
You also state Stardress mix didn't do anything to Elfman despite the fact we see him take damage from the attack. You clearly see him and Mirajane bruised from the attack. It might have not knocked them out but it did damage them.
Matter of fact they have the same amount of damage from Lion maiden as they do after their fight with Madmole and Skullion.
If Elfman was on a higher caliber wouldn't he have defeated Lucy especially with Mirajane backing him up. Even if he wasn't serious as you claim. You are overrating Elfman power and underrating Lucy. The fact you can't actually provide a panel of Elfman outclassing Lucy alone not with Mirajane just proves this.
What I am delusional about. You have yet to provide an attack from Elfman strong enough to knock Lucy out. You are saying elfman would fodderize Lucy despite the fact they already fought and it didn't happen and this is with Lissana and Mirajane backing him up. If elfman is as strong as you claim Lucy would have been defeated rather than the battle ending inclusive due to interference.
Once again what form would Elfman use to defeat Lucy? We know his Lion form can't do it as shown on panel. How is he going to knock her out.