
Tapu Lele- Win Needs Flash Cannon
A Rank

Gardevoir-Mega - Win if no focus blast Needs Flash Cannon

Magnezone - Mostly Win Needs to have Rock Tomb + Dodge Zap Cannon

Meloetta -
B+ Rank

Jumpluff - Win if taunt (and don't get totally wrecked by sleep turns) Grassium bypasses Taunt

Primarina -

Sableye-Mega -

Togekiss-
B Rank

Kartana-
252 Atk Choice Band Kartana Sacred Sword vs. 0 HP / 80 Def Heatran: 332-392 (102.7 - 121.3%) -- guaranteed OHKO
Lopunny-Mega -

Pinsir-Mega - Win

Porygon2 - Win if taunt You can actually still get KO'd before you KO them

Volcarona - Win With Rock Tomb
B- Rank

Camerupt-Mega -

Deoxys-S - Win if taunt With Rock Tomb (loses to Specs)

Kyurem -

Latias-Mega -

Magneton -

Vivillon - Win if you don't get bodied by sleep turns Requires Taunt

Zapdos - Never faced this on ladder I have no idea lmfao Lose
C+ Rank

Gigalith- Win With Flash Cannon

Heracross-Mega - Win Depends on who's faster

Latios -Win Depends on moveset

Regice - Mostly win Requires Taunt

Salamence - Beats Outrage, DDance, IDefense, Roost and scarf variants Requires Taunt + Flash Cannon

Umbreon -
C Rank

Aerodactyl-Mega - Win Flash Cannon

Buzzwole - Lose Depends on Speed

Darmanitan - Win if no Superpower (or if it's endure custap Zen Mode rofl) You eat a Superpower

Marowak-Alola - mostly win Low Kick is death

Rhyperior - Win Assault Vest eats multiple Flash Cannon and Banded/Z move Wreck you
C- Rank

Alakazam-Mega - Lose if focus blast Encore Disable also beat you, for the most part

Hydreigon - mostly Win With Flash Cannon vs Scarf and assuming you don't get flinched or crit at all-

Muk-Alola - Win if EP Taunt
D Rank

Ampharos-Mega -

Breloom - Win only if you're Timid

Lilligant - Win Taunt

Riolu - Win Taunt

Roserade - Win Taunt
Personally, I find Heatran to be way too stretched between its 4 moveslots to be worthy of A-
The fact that you need Taunt and Flash Cannon for so many matchups mean you inevitably have to sacrifice something between Rock Tomb, Earth Power, and Overheat.
This is moreso just speculation, but an optimal set could perhaps be Ancient Power, Overheat, Flash Cannon, and Taunt?
Ancient Power typically covers the Charizard combo you previously needed Rock Tomb + Earth Power for, so long as you have sufficient bulk and special attack, thus freeing a moveslot so you can get all your essentials packed in. You do sacrifice a couple of Rock Tomb matchups, sadly.