Actually, I can't find any viable weakness of Assassin Crosses other than their inability to wear a shield. Usually, they'll just cloak and try to drain your berries out while you struggle to force them out of hiding. And they simply put two edges or two quad LOD weapons and coma you to try and pick you out of Usakoring shield. Whats worse is that they can just Sonic Blow spam to finish you up. How's that for a character.
And I recently found out that Lord Knights aren't limited to just one weapon set. You may use just one type of build, but the choices of weapons are wide in variety. For example, a non-phreeoni LK (150 base dex for 450 base hit) may not use a phreeoni carded weapon for max output of damage, but they are welcome to use a phreeoni carded weapon as backup. However, with the costs of elite weapons and cards soaring at a weird rate, its not really advisable to have 2 weapon sets unless you can afford it.