Generally speaking, weapons with slow single target attacks are worst than weapons with fast single target attacks. For cleaving attacks, it does not matter so much (currently) as each cleave generally shaves a layer of enemies away so you have time to wind up another swing while the next enemies come in. Tough what really matters is to have a weapon that can hit quickly on one attack at least, so that you have time to land hits on stuff between blocks, shoves and backsteps.
The issue with the Pickaxe is that neither of it’s attacks are fast enough for that. In fact both of it’s attacks are unbearably slow, and the slowest one is the single target, which is the worst thing to have slow because you RARELY use the single target to kill a single enemy that is alone. You will be using the single target to kill a single priority target out of a group of enemies, all of which are trying to attack you, or shoving you, or Chaos Punching you.
Sure the Pick-axe, like the Executioner sword, has a bit of a step-in to the wind up attack, but on Legend, the enemies also have step-ins.
So honestly the Pickaxe and weapons like it would be much better if they were designed around their charged attacks being much faster and lower damage. This gives them a much, much broader window of opportunity for use. And the beta as it is now only exacerbates the issues I listed here.