Leadership is an extremely powerful stat, to the point of arguably being a little overpowered, which makes summons good by proxy. Definitely requires choosing the right summon, though, since they are far from equal to one another; I prefer Flame Knight or Grungendyr for reliable high damage output, or Talsenne for the greatest possible damage potential at the cost of being somewhat inconsistent (Talsenne, don't just swing your spear at people. Talsenne, Power Wave is not on cooldown, why would you do a basic attack. Talsenne, please...). If you don't use stun/prone abilities yourself, the Bear is also a good option due to having multiple abilities which inflict prone, decent damage output, and high HP paired with a self-heal.