One thing I will say is - don't claim all NN's are bad/terrible just because you've had a bad experience on 1 server's NN. Yes there are some server's who are known for having terrible NN's, but there also server's who are known for having a generally good/decent NN.

Adamantoise's NN is generally fairly decent. People ask questions and get helpful/useful answer's virtually all the time. Yes it is used as a chat channel for ppl on it, yet when I've been on I've nearly always seen them stop chatting once a question is asked... they answer it, then go back to chatting when nothing else asked. Is it perfect? Nope.

Unfortunately there are a few bad apples who seem determined to troll and spoil the game for new players who join the NN - such as doing what was done to the OP by spoiling what happens in Shadowbringers. Or they get argumentative and rude about the help offered by other mentor's, or the reason's other mentor's are there. These ppl do get kicked from the NN when they start doing this nonsense... but sadly they can just keep coming back after the 3-hour timeout expires.

But is the few bad apples really a reason to ditch the whole system? *shrugs* IMO nope, but to fix things SE would need to actually spend some time dealing with reports of shitty NN behaviour and taking action... and ensuring known trolls/pest's are unable to re-join the NN on any character on their account. Will this ever happen? Doubtful.