Having rough time finding a weapon

I haven't played the game in many years. I've loved Kruber as my main class. Back when I played Hunstman was very broken but I think they changed it. I like mercenary and I've used the halberd with him forever. However I just bought he knights grail and I'm using the weapon which comes with out. Is this the best weapon to use for him? I'm also confused because instead of a gun I get a 1h and shield now? In what situation would I swap from the 2h to the 1h and shield? I'm so used to using a gun as a secondary.

Do I have to buy more dlc to unlock a better weapon?