Ah yes...sorry that was so long ago I had forgotten that post.
I still remain to be convinced.
Let's respond to a few easy points first...
1. Please let's not consider re-enactment groups an authority

A cardinal rule of historians is to go to primary sources. Too much time has been spent over the years arguing based on secondary sources who manage to at best disagree on the interpretation of primary sources, or at worst simply perpetuate blindlylong outdated interpretations.
2. Impact foot based on warband from DBM? That's highly debatable. Have any of the authors ever alluded to that? And using debatable assumptions as evidence for your line of argument is best stayed away from. To me it seems in fact like backward reasoning. You clearly believe that legionaries should not be classified similarly to "warband" troops, ipso facto any rules that do so must be flawed. I in fact agree with you somewhat here, but my viewpoint is that imapct foor legionaries are about right, and it is the loss of a differentiated "warband" troop category that is a bit wrong.
So leaving those aside as essentially irrelevant...
3. References to "close order" doesn't really say very much. Are you seriously suggesting that any infantry formed in close order should be considered off spear (except presumably for pikemen and def spear)? Not to mention that it is a relative term, so exactly what it means on the ground is uncertain.
4. I'm not sure I like Vikings as Offensive Spear, so I wouldn't use them as comparative evidence in this sort of debate. They certainly don't seem to fit naturally alongside Greek hoplites to me. I guess the list authors feel that it produces the right sort of effect.
5. "Shieldwall" is a bit vague as well. Legionaries throwing spears of some sort and then fighting in close order with adjacent shields and controlled swordplay is a fairly standard idea throughout the lifetime of the legionary as a distinguishable troop type, but presumably wouldn't qualify as "offensive spear". (I'm reminded in this context of arguments revolving around description of certain troops as operating in "phalanx", and whether that implies they should be categorised as pikemen or not.)
Testudo certainly doesn't seem to fit the bill for offensive spearmen. Used seldom in open battle as far as I know, more so in sieges, and designed to minimise vulnerability to missiles, at the cost of decreased mobility and offensive power.
6. As far as I know, Ammianus (and feel free to provide additional quotes to the contrary here) refers to Romans sometimes retaining spears in hand to thrust, whilst still suggesting that that was the exception rather than the norm. So I don't feel that provides particularly compelling evidence for a rethink.
7. And in any case, if you are arguing for increased use of defensive tactics by legionaries in later periods, locking shields and bracing spears to repulse cavalry (and this applies to the Arrian anti-Alan countermeasures as well), doesn't that suggest in game terms def spear rather than off spear? That would make more sense to me from an evolutionary perspective too - later still Roman (i.e.; Byzantine) foot become defensive spearmen. Envisaging the transition as happening earlier than currently represented in the lists is a simpler theory than interpolating an additional evolution in a completely different direction, then back.
Other thoughts...
There is another line of argument to follow that might suggest later Roman legionaries should be differentiated from earlier ones. What does reversion to oval shields and change to longer swords say about how their tactics might have changed? I've wondered that for some time, without any particular conclusion, but if anyuthing I feel it suggests more emphasis on more open order (more room to swing the longer sword, and less point to having parallel sided shields which fit together neatly). And in similar vein I also found myself disagreeing with Phil Barker's reasoning in DBx lists - he says that detached lanciarii were amalgamated into new elite legions, and that later legionary equipment changes made them similar to the old lanciarii so superceded their function. That line of though seems to suggest to me that following his own logic he should have graded later legionaries as Bd(F), especially as he sill seems to follow the unarmoured line of thought.
Ultimately all this historical interpretation/debate is interesting, but misses the point. The classification of troops in FoG should be chosen to produce the right effect on the table.
What exactly about impact foot/light spear classification seems to you to produce the wrong effects, that off spear would fix?