First: I agree that Eichel is easily the best player of the four. He's a legit superstar if he's playing in a big market. He's a wonderful player and I'd love him in NJ. Again, if a NJ fan says the value in the trade favors Nj right now they are just being defensive. Dahlin is young and inconsistent and Hughes hasn't hit his stride yet so we can see in two years what might happen but for now of course NJ "wins" the trade, but some NJ fans are suggesting it would be a Pyrrhic victory.
Second: NJ fans had to contend with Lamoriello signing dinosaur after dinosaur at the end of his term so they saw the team refuse to try to rebuild or retool for a number of years. Sure they may have hung around the fringes of playoffs but the fanbase knew the team was circling the drain. So NJ fans saw trying to UFA and veteran stopgap your way to relevance and it didn't work. Then, Shero takes over. He promises a rebuild with patience. My guess is that is what he wanted. Then, Hall falls in his lap. The trade was one for one. I'm sure Edmonton fans still bristle when they hear that. That said, Hall only talked about winning and playing big games from the minute he got to NJ. So what does Shero do? He quickly tries to build a team around Hall. He got lucky that he got Hischier. He might have gotten Patrick. But he also made a trade with the Rangers which angered the NJ faithful to get a depth rental for a bottom of the playoffs team. That was poor asset management to cater to Hall. So at least NJ makes the playoffs year one. But then, Schneider falls apart in net as he ages. Nj is stuck with his anchor contract. Then, Shero makes deals for guys like Gusev and Subban and Mueller and Johansson, giving out second round picks like they are going out of style and none of the trades work. The team still stinks. Meanwhile, the draft picks weren't as plentiful as they should have been because Shero traded many away and the ones they made were meh (Zacha's first few years or McLeod) or just took longer to work out (Blackwood Smith and depth guys like Sharangovich and Maltsev and Bastian). So, the team tried to cater to Hall and to some extent took away from trying to find an extra top six guy or top four defender or starting goalie on what should have been a rebuilding team. And the end result? Hall won't sign an extension in NJ and he gets traded and the GM loses his job.
TLDR: NJ has had two instances of trying to build a relevant team without a good support structure of young players in place and both times it flopped. You have to allow for NJ fans to say that trading for Eichel is like trading for Hall again. Winning the trade doesn't necessarily make the team better.