The person at the end is Superman. If it was Lantern, Martian Manhunter, or Supergirl, you'd know. They would not hide a character on that level. Superman, on the other hand, has been all in the marketing and press materials.
I don't know if I buy this. I've seen Marvel stans be just as petty. People were actively rooting for Suicide Squad to fail just so they could watch DC stans be upset over the RT score. Same thing happened with Wonder Woman, and when Wonder Woman ended up being good, a lot of Marvel stans jumped to saying it was just because it starred a woman. And Marvel stans were among the first to start making jokes about Synder leaving JL, even though we all knew the circumstances.
And all these people go out and see all these movies. Make no mistake about it. The stan shytting on the Justice League or Thor trailer today will be right there in November, ticket in hand. Even if it's just so they can get online and shyt on the movie to other stans. That's why Marvel and DC are winning; people will pay money to see their shyt just to complain.