Kyria was in the Water Dragon's temple under the sea, Madmole was on a boat. Any of the Diablos guys were in the city, so it's ok that Skullrion didn't care at damage the city. Black Ash wouldn't be so effective as when the target is surrounded by a vortex of ashes that he can't touch.
I'm not saying that Mirajane and Elfman weren't a proper opponent. The thing is: They didn't show anything that could surpass a combo of attacks (Absolute Ash + Black Ash) that Silver's range of Ice couldn't overcome.
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Elfman didn't' show being stronger than Tartaros Erza. But because Erza's feats are kind of forced ( ''Because she is Erza") I will not focus on it. But, Erza Tartaros didn't really defeat Minerva in a proper fight, Minerva was in an internal fight on her mind and she wasn't knocked out by Erza so you can't measure how really superior Erza was at that time. AND Minerva is strong than she was in the Tartaros arc too. She remained with some % of the power-up received in Tartaros, defeated H-Wahl, so she is stronger than Tartaros Erza too.
Erza only got almost defeat by Ajeel, because:
1. Marin magic's stopped her Re-quip, so she stayed some time get dehydrated by his sand without doing anything.
2. Ajeel can counter swords attacks. He didn't seem able to counter physical attacks although, once that he was punched by Natsu.
3. Ajeel uses the ''sand world'', covering all the city in the sand, something that he didn't use against Elfman.
On the other way: Elfman didn't have someone stopping his magic for a while, he had a Take Over form that is stronger against sand and he fights with his hands and not swords. While Erza was totally at disadvantage he was totally in vantage ( and for some reason, didn't have to face the ''sand world'').
The fact that Lisanna (who was knocked out by Lucy twice in the 100Q) could endure Ajeel's fight until the end only shows that Ajeel didn't hit any really strong attack. Maybe Elfman's Beast Sand could stop his strong spells, but it doesn't mean that Elfman's feats make him good as Erza's.