I have to disagree.
It would be fucking dumb to reveal what they kearned now instead of mid battle. In this scenario we know that they trained something so mid battle reveal is pure hype.
No, you don't need to show everything, it's same to said that it would be dumb to show how Asta became stronger.
We could get at least glimpse of it, while we got nothing. Wait we got demon control power up that happened in so much series.
So...I don't see Asta "training" worth it...it's not compareble with Ultimate magic training.
Like you know that in
Final Fantasy 2 there was whole plot in getting Ultimate Magic...
Tabata used UM from there...and you know that was best part overall and it could be different from other shonen power up. But instead of showing a glimpse of something really interesting he showed Asta, with power copied from other demon control series. Now that made me aware, it could be Tabata wouldn't use Ultimate magic as real great power. I got fear that it would be just another "heart" from Tairy Fail, when guild members got their magic pool became larger. Still at least we saw even in Fail training, and here we got nothing. I wll wait with my final concludions about this arc, but again
Tabata, you couldn't use FF2 magic power without cosequences, while Tabata used it, and even not caring about building hype of UM at all. Now I got strong feeling, that Tabata used UM just because he needed to explaine that other guys than Asta will get power up too, but I don't see that he is interesting in that part at all. So in the end it could be just another filler magic power. If it was that great Tabata surely at least tried to show glimse of it....while there was nothing.