Erza was on the floor after being cut by Ennie because it damaged her badly, or are you saying she didn't get up immediately because she is lazy?
In their battle against Youkou, Natsu and Erza weren't heavily injured, but the fatigue from this battle was the narrative advantage from Suzaku won easily against them. The fact all the beaten wizards could fight against Viernes shows that enough time has passed to recover them to some degree.
Gajeel could keep up with LFDM speed, and Athena II couldn't. I don't know where you took the argument that Natsu was fighting with killing intentions against Athena II, if he didn't try to kill even Duke. Natsu knows that Gajeel isn't made of paper and he could have used a relevant spell that would defeat him without killing him. Natsu just couldn't do that using the LFDM mode.
Maybe Athena II with three stolen powers can be someone above Natsu LFDM speed level, but she didn't prove it, because she just defeated fatigued wizards from other battles. Your argument with the Athenas is pretty shallow because they don't possess significant feats.
The fact that Minerva was often portrayed as someone able to keep up with casual battle mode Erza's speed and that she was hitting Historia-Wahl with physical attacks proves that Minerva can keep with Gajeel and Natsu's speed in theses forms.
The problem with Lucy's water shield is that during Tartaros Arc it was an automatic shield, which appears even without Lucy's intention. However, after this arc, the automatic shield doesn't appear anymore, so it seems like it was Aquarius's last will protecting Lucy or that the Celestial King put an automatic shield to help Lucy. We don't know if she learned how to create a water shield by herself because she doesn't appear using it. The only spell shown in the Aquarius Stardress is Aquametria, which was retconned to be a water spell. However, if Lucy learned the shield, her reaction time to activate it before being hit by the explosions is still something to consider.
Why Yagdo Rigora will cause no damage to Lucy? Was Lucy's endurance put on Erza's league?
Arie's wool just prevented Cana from talking and finishing the spell, because the wool covered her mouth. Cana was already very drunk lying on the floor.
If Minerva is standing, would the wool be big enough to cover her all and prevent her from talking? If Lucy casts it on her, Minerva switches places with Lucy and starts the incantation again.
However, let me remind you, that Minerva can cast a dimensional wave to immobilize her target while speaking the incantation (and Erza and Kagura couldn't escape from it before the incantation was finished), so I think it's not likely that Lucy would be able to escape from it and prevent the spell conclusion.
It's not Mashima writing a fight where Lucy needs to win, so Minerva will be unable to use her magic properly to lose the battle (as it happened a lot of times with Fairy Tail's enemies). We're comparing the power of the two witches, their feats, and the portrait about their levels in the manga without the heavy hand of the plot helping the protagonists. Minerva's magic can deal with everything that Lucy can cast. And Minerva is faster, and more skilled as a fighter than Lucy. Minerva never would put a shield of wool to counter Kiria's strong cuts, for example.