Upon further thought, I think Luke/Garchomp could have a place in Expanded.
Not as a dominating meta deck but there are a couple cards in Expanded that makes it somewhat viable: The first being Korrina. Not only are you able to rip the Fighting Garchomp from your deck plus a Rare Candy (or whatever item you'll need next turn), it also searches out Lucario.
Secondly, VS Seeker. More reliable way to use Cynthia and hit for 230 (on EXes/GXes)? Yes please.
You could run the deck as a pseudo Sylv deck, ripping Hammers or Team Flare Grunts to disrupt your opponent but not using an attack. This keeps the deck offensively threatening while being able to play the disruption game pretty consistently.
I'm not sure if I lean towards a 3-1 split, 2-2 split or just all-inning for Fighting Garchomp...
I'll have to do some testing but I'm genuinely excited to try this out.