I read your post as well and I only agree with you in part. Apparently you did not read mine. In order to disqualify Lee two things were necessary: 1. the infraction had to be flagrant, and 2. the official declaring the disqualification must have observed the entire action.
First of all, as you point out, it was flagrant "in [your] opinion" an opinion which I do not share.
Second, it is highly unlikely that the ref "observed the entire action" or I doubt it would have been an ejection: a 15 yard penalty, absolutely, positively, without a doubt a fifteen yarder.
A disqualification in a case like this is a "judgment call." Was the official clearly wrong in disqualifying Lee? NO because in his apparent judgment the infraction was flagrant, and he thought he observed the entire action. Was the ejection mandatory, I don't think so. Read the definition of flagrant, and watch the video -- had he observed the entire actionI doubt he would have made the same decision; that is except for the fact and this is what I think was the deciding factor the refs knew about all of the pre-game hype and wanted to make certain that things never got out of hand. As I said above for that I commend them.
Bottom line: did they have to eject Lee? NO, was there sufficient justification for it? Yes.
1) The action was absolutely flagrant. Again, this is where the interpretations manual and the interpretations given by the officiating department in meetings, conference calls, publications, scrimmages, etc. are key to know. A punch like that at the face is deemed flagrant, no ifs, buts, or ands about it. There is no other way to rule it. A punch such as that is always going to be ruled flagrant if seen clearly.
2) You aren't right in your doubting. Why? Because there is 7 officials on the field. They are going to see this, especially on a punt since everything is wide open. The Back Judge is with the return man and has the area around the return man. The Field Judge on this particular play is not watching Lee and the blockers, he is also down with the Back Judge since the punt is to that side. He is picking up the blocking in front of it and to the right side of the return man (also looking for anybody stepping out of bounds). The Side Judge might see this, but he is more of a clean up on the play and might be looking up the field. The Line Judge DEFINITELY has this, especially the dead ball action as well as the Head Linesmen. The Headlines men definitely had the live ball action from start to finish. He is picking up the gunners and the blockers. Since they are engaged, he is not taking his eyes off this action. The Umpire additionally as the play clears is going downfield and since this ends up in the middle of the field he is picking this up. So on this play you have the Umpire, Head Linesmen, and Line Judge looking at this action. The Head Linesmen sees everything from snap to the end of the scuffle, the Umpire sees the end of the live ball action and the dead ball action. The Line Judge sees the end of the live ball action and the dead ball action. So you have three officials that have seen more than the entire action. The entire action doesn't mean the part he is being manhandled by the Lions. It means the personal foul act. As in, you have to see the whole punch. Not just his hand in the face of the Lions' player, but anyways you have at least one official that saw everything from snap to finish and two other officials that saw all the dead ball action. I would be my life on it that the entire action was observed because that is simply the mechanics on a scrimmage kick for 7-man officiating.
3) You are right. A disqualification is pretty much always a judgement call, unless they do something such as come off the sideline to participate in a fight, strike an official, or do something absolutely outrageous. You are right they must deem it flagrant and that is a judgement call. However, they base that judgement off the interpretations given by the NFL officiating department and everything they had learned up to that point. So yes it is judgement, but they really don't have free reign. They have pretty stringent guidelines.
4) You are right, nothing required them to eject Lee or even flag him. However, if they didn't, you better believe they are going to get marked down for it and get hammered by the evaluators. Last thing an up and coming Line Judge wants is to find himself in the bottom % of officials on their evaluations because his NFL career will be over. Contrary to hysteria, NFL officials are held to an extremely high regard, the highest out of any sport. There is no union like MLB that you cannot be fired unless you do something ridiculous or are clearly not capable of being an official. In the NFL, if you don't perform, you are done as an official. This includes enforcing their rules, and more importantly their interpretations and mechanics.