How can I improve my Character Card sets?

My main is a Hero.

Here are my current cards:

Hero (DEF +5%)
Paladin (Some stupid +damage per level that makes no real sense)
Dark Knight (MaxHP +5%)

Xenon (40 STR/DEX/LUK)
Demon Avenger (5% Boss)
Demon Slayer (5% Stat resist)

Crossbowman (4% crit)
Cannoneer (-5% exp loss)
Kaiser (80 STR)

This also gives +15% Boss, 15 att and 3000 HP/MP

+10 all stats from resistance
+10 all stats from explorers
10% HP-> damage from 3x warrior

I'm happy to level up any other characters to improve these sets. Any suggestions? My primary concern is the Cannoneer as it is the only one which doesn't really give any major benefits, but I can't see what to replace it with.

Ditch cannoneer for kanna. Ditch hero for hayato. Replace paladin with DS/DA. Replace DrK with DS/DA. Replace DS/DA slot with cannoneer, and DS/DA slot with a mechanic. You gain at minimum pirate set eff, 6% min crit, 3% boss, 15% buff duration, in exchange for 5% def, paladin eff (insignificant/does nothing), warrior set (insignificant/does nothing), 5% HP (main is hero; can live without it).