Yeah, Disciples of Magic can use auto-attack like melee classes, it's just not set by default on the hotbar, so you have to open the Actions and Traits menu and set it manually onto your hotbar (in Actions and Traits it's found in the 'General' section, the same place Limit Break and Sprint are found for instance). As has been stated though it's not very effective, but early on and especially while soloing, it all adds up.