Did they truly face him? Perhaps, but if they did, they "faced him" in the sense that "they tried to stop him but failed miserably and were stomped". Much like Present Zamasu "faced" Beerus.This is a false argument. The Z-fighters did face Infinite Zamasu, sensed his power and Goku, Vegeta & Future Trunks were abled to deflect one of his mouth blast. There's no reason to dismiss Vegeta, Goku and Shin's claims about Suppressed Jiren>>>>any previous enemy outside of bias.
Goku after his first fight against Zamasu admitted that he is much stronger than the Supreme Kai of his universe a.k.a. Shin. For a Kai, Zamasu was very strong. He was a natural prodigy and a fighting genius, and according to Goku, if he kept training, one day he could rival even Beerus. Shin himself in the manga described his skills as an apprentice almsot certainly peerless in comparison to that of the Supreme Kais. The Supreme Kais himself recognized Zamasu as a genius. After all, Zamasu was a simple North Kai, yet he was chosen nonetheless by Gowasu despite his very low status in the God hierarchy.Present Zamasu was about SS2-level, Shin is probably SS1G2-level
Zamasu's faces covering the sky are just a physical representation of his soul becoming part of the very fabric of the cosmos. To defeat Infinite Zamasu, Jiren would have to find a way to actually destroy the very fabric of the cosmos, which:He would punch the sky.
A) Would be impossible, since only Zeno can eliminate immortal beings;
B) Would be impossible, because if you destroy the fabric of the cosmos, you destroy the cosmos itself.
Well, at that point, Fused Zamasu was breaking down both physically and mentally. His body was falling apart and was damaged by all his fights against Goku, Vegeta, Trunks, and Vegito (his regeneration capabilities were still strong, but flawed). And mentally he wasn't thinking very clearly, he had gone completely insane and had lost it. So obviously Trunks merely caught Fused Zamasu at his most vulnerable point.What about the fact that Merged Zamasu was easily done in by Trunks after absorbing the Spirit Bomb whereas the suppressed Jiren was able to force back the Spirit Bomb that was being pushed by Super Saiyan Blue Goku with the Kaio-ken x20?
If Trunks had fought Zamasu as soon as he gained his power-up thanks to the Light of DIvine Justice, so before the fight with Vegito and before he sacrificed his speed to become stronger, then I think that Zamasu would have defeated Trunks, even if he had the sword of love and friendship. If you look at Fused Zamasu in his final moments, his main problem wasn't the lack of strength, but the lack of speed. He simply couldn't keep up with Vegito and Trunks because he was too big.
And also the sword merely cleaved Zamasu in half. It didn't actually destroy him. Zamasu destroyed himself. As Gowasu said, He willingly cast aside his divine vessel to merge with the very fabric of the cosmos and become his very idea of justice and order made manifest. It wasn't Trunks who obliterated his body. At least that's what I think happened considering the fact that Zamasu kept talking even after he was cleaved in half, and his body disintegrated only after he stopped laughing.
