I think that's a perfectly valid point of view, and some of those aspects and feelings were likely present.
But you can't just "snap" and declare an emergency because you've had a long flight, had to hold, don't like the runway assignment, or face the possibility of sitting in the penalty box waiting for a gate. Those are the day-to-day realities of operating within the NAS.
That doesn't mean it doesn't happen. Everyone has bad days, everyone has lapses in judgement, and everyone does things that they'd do differently if given the opportunity. Maybe this guy had a bad day and regrets his actions; maybe he still feels justified. Who knows?
Either way, it doesn't excuse the behavior. All of the factors you mentioned could have been mitigated in one fashion or another, without resorting to what he did. The chain starts well before he checked in with tower.
If he can't handle sitting in the seat for 5 hours, he should have bid another line, or another aircraft. If this was just a transient issue, he could have called out "fatigued". If saying "minimum fuel" didn't get anybody's attention, "emergency fuel" would have. If he didn't like the possibility of getting 22, he should have told Approach that he couldn't accept it so they could pre-coordinate. If it wasn't until final approach that he decided he didn't like 22, then he should have gone missed and requested 31. If at any time during this excercise some other factor necessitated an immediate landing, he should have declared an emergency and stated the nature of the problem. Failing all of that, he could have filled out a company JSAP report, an ASRS report, called the TRACON or Tower on a landline, called his Chief Pilot or Flight Standards people, or even called the FAA Safety Hotline.
But it's hard to believe that some unforseen circumstance caused him to declare, because he made the explicit threat to do so based solely on the runway assignment only a few moments before. He had this in mind long before he keyed the mic to say it.
So I think you're right, this entire incident is really just the culmination of stressors and the manner in which the crew chose to deal with them. My personal opinion is that they should have done it differently.