Mewtwo is cool once it gets setup, but how often will it get setup, and they have a chance of beating you on time (they probably have a prize lead on you).
Machamp is cool, but once again kinda hard to setup, and his weakness kills his efficiency.
Like Machamp, donphan is only effective if you play more than one. Most luxchomp's can kill it once, but twice or more is really diffucult.
Promocroak and Ambipom are pretty good, but don't expect an autowin just because you play them.
Fan Rotom gets killed way too easily and takes too much energy.
Draggy's cool on paper, but it forces you to waste a poke turn once your done, not to mention the fact that it takes a DCE and an Energy Gain. Plus it can just be counter killed by garchomp's earthquake.
Rapidash is just like mewtwo, only worse because they can still hit with uxie x or other attackers (they're bound to have a couple).
In the end, there aren't many techs that effectively counter luxchomp. Decks, maybe. But not techs.