Hm, I would give this to the Berserkers around low to mid diff. It depend really , if 100 attack at once then it will be low diff but if its 1 on 1 , 2 on 1 , 4 on 1 like in the GmG arc then i would give the benefits of the doubt that Erza will lose at around mid diff ,but hey ... That is already impressive right ?
In my opinion , Erza lack the Hax, Aoe and Attack potency to defeat 100 of them beside that the Berserker is not weak either. The sheer strength of one Berserker is strong enough to throw on guard Erza flying to the back as shown in here ...
And not just that, their combats abilities is upgraded high enough toover powers literally everyone In the battlefield. Even tho this is debatable due to their stamina.
Not to mention their durability and ability to not cares or feels pain

definitely hard to even took one down.
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Yeah, most people don't realize that Erza's
Nakagami Starlight can take out a quarter of the army or more. The only reason she was struggling was because she was low on energy and focused on defending Makarov. In case nobody noticed, she wasn't wearing any armor. That red pants and bandaged "armor" gives off no magic power as stated by Ikaruga. So Erza technically wasn't using her magic at all.
Not to mention, I see some people say Erza would lose to the berserkers more easily than someone like Ajeel... That's absurd unless you think 100 Berserkers > Spriggan? Why does Zeref need his Spriggan 12 then? All he needs is for Eileen to make an army of berserkers... which is in fact weaker than what he has right now.
Where did you gets that nakagami starlight can took half of the army? Do you means the one million army? Then nah or do youmeans 100 berserkers? Still nah tho lol. She just don't have the Aoe. Maybe she will took down 10 people with it if she use nakagami armor right after the battle started.
She don't have the mp feats that says she could use nakagami starlight more than once, I'm giving the benefits of the doubt that she will be able to use it twice if she use it right off the bats.
You're right that erza red pants armor don't have any magic but you're wrong if you think that her attack didn't use magic. She use it, the magic is in her swords.
Yeah ikaruga did said that the armor don't have any magic but it's said that she puts all of her magic in her swords to make a powerful attack.
It's later made clear again the power of red pant armor in her fight with azuma
So basically Erza red pant armor attack is Erza strongest attack after Nakagami starlight and this attack did basically little to nothing to the berserker as we can see here
Well, I think even with immense magical power as you implying... Ifshe still can't do anything. It's still no use.
100 Berserkers is too much for Erza.
P's. Accidentally deleted my post .