Just saw the usage stats and it made me curious. What ev spread does Moltres run that it gets killed by two gunk shots from Cinderace with slight chip? Because really, that never happened to me even when it gets poisoned and I used to spam Moltres a lot
Generally there are a few speed benchmarks for Moltres to look at first. The slowest would be hitting around 230, which gets the jump on Choice Specs modest Magearna, slow Landorus-T, and the rare Jolly Crawdaunt. Outrunning Specs Magearna is the main selling point here, which can otherwise hit-and-run with Volt Switch easily. Alternatively, you can hit the mid-250s (254-256) if you want to outrun Jolly Shift Gear/Choice Specs Magearnas, modest offensive Heatran, the rare Bisharp/Tapu Bulu with an adamant nature, and Diggersby (this one hits 255, which is why I included a range above). Finally, I have seen some fast Moltres, getting the jump on Excadrill, Nidoking, adamant Urshifu, Rillaboom, jolly Heatran, and offensive Togekiss, but this is a bit less common. The rest of the EVs can go into defense, but at times there is a little thrown into SDef to help with Magearna, Heatran, and other special attackers it commonly interacts with. For the sake of giving you the benefit of the doubt though, let's say it pumps out PDef for things like Cinderace. Here are the relevant calculations:
Assuming 230 speed Moltres...
252+ Atk Libero Cinderace Gunk Shot vs. 248 HP / 204+ Def Moltres: 160-190 (41.7 - 49.6%) -- guaranteed 3HKO after Leftovers recovery
252 Atk Libero Cinderace Gunk Shot vs. 248 HP / 204+ Def Moltres: 145-172 (37.8 - 44.9%) -- guaranteed 3HKO after Leftovers recovery
You are one poison or any residual damage away from being in danger of outright losing to adamant. Jolly gives you a little room, but if rolls do not cooperate or you are not at exactly 100%, then it becomes risky business as well. This also means that Moltres is forced to Roost each time this sequence occurs and any other time it is to take damage throughout the game if it wishes to remain in tact to check Cinderace, which is a counterproductive strategy itself and likely indicates you are better off going with a more practical check/counter to Cinderace.
Assuming 256 speed Moltres (or anything faster as the calcs only get worse for Moltres defensively)...
252+ Atk Libero Cinderace Gunk Shot vs. 248 HP / 100+ Def Moltres: 178-210 (46.4 - 54.8%) -- 10.5% chance to 2HKO after Leftovers recovery
252 Atk Libero Cinderace Gunk Shot vs. 248 HP / 100+ Def Moltres: 160-190 (41.7 - 49.6%) -- guaranteed 3HKO after Leftovers recovery
At this point, you either lose on the switch-in or barely avoid doing so, but the margin of error is so slim that a single poison or any other damage at all tilts this entirely in the other direction. Moltres does not even resemble a Gunk Shot Cinderace check at this point.
I think your question overestimates the defensive presence of Moltres, unfortunately.