1. Ajeel didn't fight DeS Gray to no sell anything. They didn't even really fight, They had a brief exchange, where Ajeel countered Gray, that's all
2. Darkness Gray >> DeS Gray
Darkness Gray, in his base, low diff'd Invel, while Invel > DeS Gray
3. Erza was able to block them with bare hands, with her hands charring and cracking.
And, what if she does? Erza's body is far more durable than any of her armours, so this doesn't really matter.
This only seems weak, if you downplay Erza to begin with. Erza is arguably the most durable member of the guild.
Dude, can you, for once, argue in good faith?
Wendy could literally counter Haku's hax, his greatest asset. And you're here asking how it's a type advantage.