If you have problems with Mergen’s long cooldowns, you can try Hackapell on rank 8. As a mounted class, Hackapell provides good pet bonuses, boosting ATK (OHSword+gems), HP (Pet), DEF (Pet+Shield), MDEF (Shield) and ranged debuff (Pistol+Leg Shot). Hacka skills are not impressive, but have lower cooldown than Mergen’s, so a Fletcher+Hacka becomes a sustainable damage option.
Just keep in mind that some classes and skills force you to dismount, but you’ll be fine with Archer 2 - Ranger 1 - Wugu/Scout (no cloaking tho)/R2 - Fletcher 3 - Hacka