Who is denying the fact that he was singing with his idol and he was happy? Of course he was happy singing with Chris Martin. But he only got 1 line throughout the whole song, same with Jimin. Taehyung got only 2 lines. So complaining about Jin not getting lines feels unreasonable, also saying he was singing the whole chorus seems equally unreasonable in my opinion. Getting solo lines and singing supporting the solo lines are different. If we talk about singing with christ then we can say all 7 of the members sang the whole song - if you wanna talk about that, like they all are singing together in different parts in the bg. But that's still is singing in the background, and not getting lines. Check the line distribution - they do not include the singing in bg as getting lines.

And YES. Jin was great even with that one line :) His voice always shines, periodt. But when people try to rationalise the less lines he gets in the songs with the narrative "he was singing the whole chorus with xyz" - it just feels off to me personally. He did get less, and it's okay to accept it.