This is sooo true. If internet carriers were preferring some kind of content, or censoring or giving less bandwidth to certain content, or charging for certain content - and this was causing the problems described in the mozilla article - then yes - we could have legislation to solve that problem.
What gets to me about the net neutrality movement is that the legislation they are pushing for is based on vague fears and panic. Caring about net neutrality has become some sort of weird silicon valley techno-virtue signaling.
If ISPs start behaving badly or restricting free speech, I would be happily on board to having legislation to address that. This has not happened and there is no evidence that there is any imminent threat of this happening. Net neutrality legislation is a solution to a vague non-existent speculative problem.