What would be the best MH mythical skill for a chakram user?
Whatever you want. Cosmic orb is a good one though since it hits so rapidly and has high DMG and easy to proc via chakram.
It depends on what build you want. Earthquake is great. but cosmic orb is more popular.
If your in their face, arc definitly, if you prefer distance cosmic orb is probably better
CosmicOrb is both in your face and distance.
Arc does more damage in a single hit
CosmicOrb does more DMG overall when 10-20 hits per second. Although arc does so much DMG overall when 5 hit but I would have liked if 5 arcs hit one enemy for PvP maybe and PvE sometimes.