Too much work. The debate happened back when these forums were brown.
None of that was ever hinted to be the case tho. Like no one even talked about her souls being dwindled and her being nerfed. She also still has Sitri which way stronger than BSS yet still was nerfed to not using it lol. Natsu and Erza are pretty much the only ones who got heavy nerfs and that's bcs they can't access the PoF they used in Alvarez. Natsu was inconsistent as hell in the WDG arc when he failed to produce fire magic in water despite vaping a a huge lake with his body heat from an indirect attack.
None of that says magical power which is the Power Level system of the manga. It says far more powerful than the magic she has not that it has more magical power than her. Brandish doesn't know why she can't affect END which is why she made a hypothesis. The author knows which is why he states what END's power is. If it was power level than Mashima would have steaight up said Natsu walked through timestop bcs Natsu was more powerful than her in his END form.
For Neinheart it was Irene's enchantment. We know this because she already sensed Neinheart's mp was greater than her own and would have knew that her magic wouldn't work on him. She wouldn't try her Command T and be surprised that it failed if it was PL lol. She says how strong has Irene made him, not his magical power is too high for her Command T to work. We already know Irene's hax can counter hax since the versatility is nigh endless as well. Why would it be counter productive? She just buffed him with enchantments and one of those enchantments stop Command T.
Except he can't make his magical power go below his base (which his base is still far stronger than Brandish mp). Especially when he is his battle mode still. If she can't use it on people with higher MP than she wouldn't be able to use it on August in the first place.
How so? The etherious should all disappear along with Zeref. The sole exception being Natsu, who Lucy rewrote. In Mirajane's own words, she took over Seilah to prevent her from dying. Well, Zeref dying means that Seilah dies too. Mirajane had 3 fights now. Not once did she use Seilah or any of her etherious takeovers. She was even defeated, and still didn't use any of those takeovers.
It doesn't even matter. Brandish couldn't effect it because it was more powerful. END, being a demon, should have curse power. I don't know why you think he doesn't have either magic or curse power. It says far more powerful than any magic she has btw. For Neinhart, it said magic power. Brandish simply didn't realize just how much stronger Neinhart was until he started flexing his powers. Maybe Brandish can still effect people slightly stronger than her, but she can't effect anyone far stronger than her.
August doesn't have to lower his MP. He just has to not resist Brandish's attempts to heal him. We've seen stronger characters allow magic to work on them, only to resist it later. White Witch is a perfect example of this. She can use her White Out on Mercphobia when he lets her, but she can't just go up to the other god dragons and white them out.