Ok, first off, the Spriggan do not all have the same MP. That's absurd...
Wahl has a way more MP than Neinhart. Invel and Bloodman have way more MP than Jacob.
I don't know where you fact check your information, but nothing adds up.
The Spriggans were said countless times to have similar MP. The only difference between them (like I said before) is their other stats. Neinhart has low durability which is why he lasts a lot shorter in a fight compared to the other Spriggans.
How can a mage on Brandish's caliber manipulate God Serena's magic at well, if she feared Neinhart's MP, who has exponentially lower MP than one of God Serena's powerful spell?
Enhanced Neinhart was still shit. Natsu two shotted him and he looked like a fodder.
Where you go wrong is you think Enhanced Neinhart's MP > The MP of 1 of God Serena's spells.
The truth is, the MP of 1 of God Serena's spells > Enhanced Neinhart's MP.
I assure you that Brandish is not on the caliber to control or manipulate God Serena's attacks at will.
This is really becoming repetitive...
God Serena's spells don't have more magic power than Enhanced Neinhart himself... He has more attack power. Your statement is the equivalent of saying that God Serena is using all of Neinhart's MP when he uses his spells which is totally illogical.
Natsu was able to destroy this fodder because of his low durability... I've said this before.
If my explanations aren't making sense, let me show you my reasoning quantitatively.
Let's assume God Serena's magic power is 10,000. Given that Neinhart is comparable to the other Spriggans in MP, his would be around 7,000.
When God Serena uses an attack, he is only depleting his energy by 500-1,000. So can you tell me that... 7,000 < 1,000? Or would it make more sense for 7,000 > 1,000?