Yeah, maybe I am looking too much to late game, but it shouldn't be ignored just because it's late game. That doesn't mean it can't be balanced or shouldn't be looked at, specially in these large games where we will hit late game. To only balance for the start is to play into a folly, but it is the same that the opposite is just as true.
Hold the Line is a wonderful skill, no doubt, and its a big reason to be a knight. I fear that it may just be the only reason is all. A knight is suppose to be a class that can laugh off melee attacks, they do, but yet other classes can do it just as well without any of the problems that cone with being a knight, and in cases even better. Knights still win out at are denial hands down however, I make no bones about that.
You're very right about the swords, it's a good reason to be a great knight. It draws us back to "be a knight if you want the skill to be a great knight" as the main and only reason to be a knight however. Give armored (or some approximate, weaker skill) back and then there is a good reason to be a knight if you want to tank.
All of the below is true, but there is still advantage in not needing nullify in the first place. One could instead get Guard, or Blossom, maybe Fortune to help the character guard others better, be better, or take hits better.
Overall, I agree with what you said in the most part, but I fail to see how it is any different than what I've been saying earlier. Unless you want hold the line, or be a great knight, there's sadly little reason that I see to be a knight in a game that hits promotions.