Honestly, in this deck, you are perfectly fine with doing two hit KOs once or twice a game. I've been playtesting this deck quite a bit at my local league, and with ascension gabite and BKP garchomp accelerating energy, two hit KOs are not a problem, freeing up turns to use other supporters besides Cynthia. The deck plays much, much better with a 2/2 Garchomp split from my playtesting. With a strong energy and a choice band (which are super easy to get in the same turn) you OHKO a zoroark GX and accelerate any energy you want from the discard pile. Play one devoured field, and you are OHKO all of the 210 HP mons running around without a band.
Here is the list I have been testing, with a lot of success:
Mons (21)
4 Gible ULP
3 Gabite ULP
2 Garchomp ULP
2 Garchomp BKP
3 Riolu ULP
3 Lucario ULP
1 Remoraid
1 Octillery
2 Tapu Lele
Supporters (12)
4 Cynthia
2 N
2 Sycamore
2 Guzma
2 Brigette
Items (16)
4 Ultra Ball
4 Rare Candy
1 Evo Soda
1 Pal Pad
3 Choice Band
2 Super Rod
Stadiums (1)
1 Devoured Field
Energy(11)
4 Fighting
3 Strong
4 DCE
Matchups:
Zoroark/Lycanroc is a cakewalk. Easy win. Unless you brick and brick hard you should never lose.
Buzz/Lycanroc 55/45 - If they hit those max elixirs, this can be a very difficult matchup. If they are playing BKT mew it's easily 35/65 in their favor since they can just one shot your Lucario with a choice band. Killing the strongest part of your engine and forcing you into a seven prize game.
Garbodor Matchups 50/50 - Ability lock can be a PITA, but honestly, it's not that bad. Drampa Garb can be a pain (I'd put it at 40/60), but you can one shot Drampa easily with a BKT chomp, strong energy and devoured field. You can also try to two shot the garb with ULPs Chomp and a DCE. Espeon Garb is not bad if you can get an ULP Chomp powered up.
Bulu - This is a difficult matchup. Probably around 40/60. IF you can pick off a Volt early, and keep him off the field it is winnable since Bulu can't one shot without discarding. If you can't you lose. Bulus is just too fast to keep recycling Garchomps.
Gardevoir - 35/65, The weakness doesn't make this an auto loss as much as you might think, but you have to draw like fire the first two turns to win. If you can't get out at least 2 Garchomps turn 2 with Gabites on the bench to be evolved turn three, just scoop. Unless Gardy also has a bad start, then play out another turn or two. You can one short Kirlias with BKP Chomp and a Strong energy, and Octillery with a Devoured field. THANKFULLY Gardy is dropping in popularity like a brick in water.
Metal Variants - Every one I have played that is already testing out new metal variants it's been 50/50 or better for lucario garchomp because of how well it can trade KOs.
Luxray - Fairly easy match up. Item lock is not a big issue for this deck thanks to Lucario and Ascension due to Luxios lackluster damage output, and the lack of support to do supplemental damage using poison and burn.
