They would be relatively around the same level form their initial interaction with one another with how they faced off with one another, Irene struggled because of Wendy being an Enchanter herself and using DS magic to stagger her as well, which Irene still won in the end regardless, and she managed to even push Acno back even and even dodge his attacks too. Erza and Laxus are roughly the same level of strength with Laxus being slightly stronger, but not enough to put down Irene where he even struggled for a bit against base Wahl for a while.
Just because two characters are portrayed to be around similar level, they'll face same difficulty in facing the same opponents? Ridiculous logic.
Eileen struggled against Erza, while August didn't against Jellal and Gildarts specifically because of the way August's magic works.
"But Wendy helped" yea, in round 1. In round 2, when Wendy was out cold, Erza still held her own against human Eileen. So no, you're wrong. Human Eileen hasn't shown any impressive physical combat skills, she's more of a ranged caster type.
"Being around same level" overall means little, when how the powers themselves work makes a lot of difference.
Neinhart had a far easier time dealing with Erza than even Eileen, because he just outnumbered Erza with his summons, and Erza lacks AOE to deal with numbers. Dimaria, for example, can one shot Erza if she has enough MP to use timestop on Erza. While Wahl would likely lose high diff against Erza.
Neinhart, Dimaria and Wahl are portrayed to be on the same level overall. Yet, one low-mid diff'd her. One will one shot her. While the other will lose. See the difference?
"Eileen pushed back Acno"
Yeah, and? Pushing back jobbing non serious Acno is supposed to impress me? Jellal upstaged those feats by the way.
Also, Laxus was stronger than Erza by a decent margin in x792. The gap only closed by x793.
Human Eileen was on x792 Erza tier in all stats except magic power. x792 Laxus will give human Eileen a serious run for her money.