The true power of this card is generally the extra attack. A 5 strength extra attack is a powerful ability for an event. Especially when playing defensively or having an attrition war in the middle of the board, Battle Leader is one of the key ways to get advantage or comeback, being both an economic and tempo advantage.
However, especially against some decks, it is hard to make use of without exposing your summoner unless you also have Marshal Forces or Stronghold ready to go. And then you can see how sometimes it requires too many things to go right to be useful.
In brief, this is a very powerful event that when it finds its moment is one of the key ways the faction gains an edge, but clogging your hand to try to find that moment in a game that is not leading in that direction may not be worth it and it is then better to discard for other cards.