No Dark Side GL can efficiently counter a JMK/CAT squad.

@ThomasClarkeT90 I'm seeing a fair few Lord Vader's climbing and beating back JMK. On my shard JMK vs JMK is preferred as it is quicker to mirror than to use Lord Vader. 

However, this is feedback and not a technical issue and should be posted over on the official forums: https://forums.galaxy-of-heroes.starwars.ea.com/