Personally, I think that Ajeel is like Zancrow-type or Jackal-type. Talks a lot of shit, but when it comes to do something he is weak. And that was the first wave of Zeref's invasion - still we haven't seen August, Dimaria, Serena and Invel yet. Of course I do not mean that the first wave is the weakest, 'cause Brandish of course, but Zeref is not going to reveal all aces up one's sleeves. xD