The Knights mark punishment is very trivial to avoid. That is the entire argument I've been making.
The Knight's mark punishment is no easier to avoid than the Fighter's.
They are a little different, though: The Fighter's Combat Superiority is better than the Knight's OA (even in Defend the Line) /and/ better than his own Combat Challenge mark-punishment. The Knight's mark punishment is better than the Fighters, and better than is own OA. So if a monster has the choice of staying where he is and hitting the Fighter's ally, vs walking around the fighter and doing it, he'll probably stay and take the marked punishment - and, once he does, all other enemies the fighter may have marked are no longer under threat of mark punsihment, and can attack his allies freely. Conversely, if an enemy has a choice of attacking a knight's ally and taking the auto-damage-on-a-miss mark punishment, he might just move away, provoking an OA - because, hey, it might miss. And, every enemy will face that choice, because both mark punishment an OA are 1/turn, not 1/round.
How individual DMs will respond to that quandry may vary. With a single enemy, it might well lean towards taking the fighter's mark-punishment (because it's not as bad as provoking an OA), and taking the Knight OA (because it's not quite as bad as his mark punishment). But, the Knight's stance-enhanced OA is better than the Fighter's bog-standard MBA mark-punishment. Faced with multiple marked enemies, the quandry is different. If one enemy 'takes it for the team,' the threat of the Fighter's mark-punishment is ended, just like that. There's no such option with the Knight, so it's respect the aura, or everyone provokes OAs. And, it's a quandry the DM of the Fighter faces at most once per Close Burst encounter or daily power the Fighter has, while the DM of the Knight faces it any round the Knight stands next to several enemies, or enemies end up next to him in some other way...
I think what you're trying to get at here is that the case of one or more monsters being able to forcibly move the party defender away from anything it marks is so common, that the only /real/ effect of a Fighter's mark is the -2. That the Fighter's mark punishment is meaningless, so the fact that the Knight has a much easier to establish and strictly superior meaningless mark punishment is, well, meaningless? Paladins, whose mark-punishment can't be so easily evaded, must be just made of glowing radiant awesome, then.