Did I say that I didn't like Matt?
Matt's been dead weight since season 2 started. He was kept on because the writers like the actor, so even though his S1 storyline was over, they made up a brand new storyline which was completely unrelated and led us only to hypocritical daddy issues and the Nightmare Man, an expendable villain. Keep in mind this only distracted and took development time from the main plot, which suffered because of this inexplicable need to service Matt Parkman.
And my other problem with them giving Matt was the way they empowered him. They ignored the careful balance made between telepathic abilities, and the great respect the show had for the human mind and made him a full out telepath. The problem with that is that it leaves with an endless array of 'why didn't Matt just' moments, where the only reason that the plot continues is because Matt forgets about his power. I mean, honestly, why is Matt waving guns around when he can make Danko do whatever he wants? Why would I need to waste any time asking Usutu questions when I can get it all immediately?
Did I mention that the whole Daphne thing, which was all that came from the spirit walk, was yet another brand new unrelated go-nowhere storyline?
Matt. Is. Dead. Weight.
And the time, that the writing staff spends making sure his go-nowhere storylines are, as you put it, "the only character since season two who's story arc and character development has gone some great places" -- should be time spent turning "annoying" characters who are actually important to the story: Claire, Maya, etc, into characters that have great character development. Every minute spent on Matt makes the show as a whole worse. That is my logic, that is my conclusion. Feel free to examine or cross examine the logic therein.
But I like Matt, for some of the same reasons you do. His storyline and character development being enjoyable in isolation doesn't change the fact that he's weighing the show down and making it worse on the whole.