You help the Tieflings and are good or you murder them all and get betrayed / punished because you are bad. Larian themselves even put it that way in their last update. The only other "option" is a failsafe for when absolutely everyone is dead and I'm not sure if that even exists.
If you are right ... you will have no problem to answer me this few questions:
1) I decided to persuade Druids to stop ritual ... my diceroll failed, and i killed them all ... therefore i helped Tieflings ... am i good or evil? 2) I decided to side with Goblins and i killed Halsin, but at gate i reconcider and betrayed them ... therefore i helped Tieflings ... am i good or evil? 3) I decided to steal the holy idol to give it to Tieflings, so they can sold it and pay ressurection for Arabela ... Druids killed Tieflings ... am i good or evil? 4) I decided to persuade Tieflings to escape ... my diceroll failed, and i killed them all ... therefore i didnt help Tieflings, yet i killed Goblins and saved Halsin ... am i good or evil? 5) I decided to not get involved between Druids, Tieflings and Goblins ... i killed Githyanki, stole their artefact and go search for Creche (not implemented yet i know) ... am i good or evil?
Since you tell me that there are only two paths, i bet you will have no problem to decide those situations. Ofc. you can simply admit that there is more.
1) Good 2) Good 3) Failsafe / Evil (you say nothing about the goblins) 4) Failsafe 5) Unimplemented neutral path
This is a video game with quantitative data so Larian cannot take these nuances you make up in your head into account. They say good / evil is 75% / 25% because they checked all gamestates and noticed an X amount of "the tiefling party happened" and "the goblin party happened" states. All of this other stuff you mentioned is irrelevant window dressing, and a third path where the party goes "well, we fucked up, all of our leads are dead" does not exist as far as I know.
So again; you can make up as many of these nuances and permutations as you like. I play a pragmatic evil character that saw Halsin as my best bet as a cure and thought the Absolute was probably a sham, so I helped the Tieflings. This makes be good because "the tiefling party happened" checkbox is marked in my playthrough. Whatever else I tell myself or even what I do besides the Tiefling / Goblin choice does not matter.