How do you know that the Dark Lord ending is not the "true" ending, if any of them are? With no later game, and one unlikely to ever happen, there's no knowing how Dark Souls 3 canonically ends, if any ending is canon. It's also not a "bad ending" just because Londor wins; this would imply that Londor are unquestionably the "bad guys" and there's really no such thing. Personally I think the Dark Lord ending is the best ending for humanity by far! The "link the fire" ending doesn't accomplish anything, you just pushed back the end by a little bit more (unlike in Dark Souls 1 the relit flame isn't even very strong, so you probably barely did anything at all). The end of fire isn't really much better, just letting the world go dark with the implication that the flame will, one day, return... and the whole sorry cycle just repeat. Again, not much really achieved. With the Londor ending you're doing something -new-, giving humanity a chance to exist beyond the reach of the Gods and their selfish acts. No longer are humans slaves to the will of the gods, forced to carry out the path they set in order to cling desperately to their own faded power. Londor is considered sinister and untrustworthy by everyone, not because they actually want anything evil, but because they want to throw off the status quo that everyone else is too comfortable with to see how bad it is for everyone.