eh, this is a hundred or so years before the hobbit, remember, so sauron is still pretty weak, respectively. he DOESN'T have the one ring, so he's weak from rebuilding himself and he's weak from being gimped without his ring. a HUMAN killed sauron. WITH the ring. a HOBBIT destroyed sauron. while silmarillion goes to great lengths to identify power levels, the entire point of the hobbit and lord of the rings is that power levels don't REALLY mean much when you're factoring in courage and hope
Not going to get into a lore fight with you, but I'll point out your two glaring errors and leave the table.
1) Sauron never dies until the ring (his essence) is destroyed. He is defeated and his will dispersed when he initially loses his sole focus of his essence but he never dies. He's a part of Arda (Earth) as a minor aspect of nature (death) and can't die until is his essence is rejoined with it (through the destruction of the ring). It's pride that defeated him (by proxy of putting most of his will into the ring), Isildur only exposes it (depending on your interpretation, maybe not even intentionally - ie chance).
2) The Hero of the LotR, like most of Tolkiens great dramatic points, is Chance / Deus Ex Machina. Not a hobbit (unless you consider Smeagol being a river folk close enough). If you're referring to Bilbo, he fails at the end of his mission and Sam (who should have been the redeemer) also fails his master and himself. Smeagol dies, by chance falling into the pit - neither of the supposed-'heroes' take any action to force him into the pit. He quite literally slips to his own death and causes the destruction of the ring and Sauron.
You're saying apparent might doesn't matter in the face of hope and good naturedeness (because God saves) is the theme (which you're right, it is, but don't confuse that with mortals defeating Sauron).
Your argument for the game comes down to he's weakened by his dispersal and loss of his focus (ring) and hope a deus ex machina saves the day again (ie faith in God) which is directly contrary to the motives in both games. Regardless, he has enough essence (minus his ring) to gather his armies and control their will to rebuild Mordor which is supposed to retake the entire time up to the Hobbit; a status that justifies the state of the orcs/Mordor, his ability to manifest in person in SoM/SoW, and lends credence to the importance of Wraith/Talion halting his return
OR he's not at full power and somewhere between his defeat and his eventual reappearance in RotK and shouldn't be in the game at all. You can't have both and say it's true to the lore, hence why you should treat it as a separate work entirely for the many other reasons the story doesn't work under serious critique.
The only active deviants during the games' time frame should be the wyrms, Balrogs, Shelob, Ring Wraiths, werewolves/vampires, and (uncontrolled) orcs/goblins/trolls/random unmentioned horrors and minor influence from Sauron.