Yes, I am aware of those as well. From what those sources say and hint at, there indeed may be a discrepancy between the Phoenix performance currently in game and the one stated in anecdotes of those you've mentioned, so I can relate to your point.
The problem HB and ED are facing, however, is that they require hard numbers and stats to implement their missile simulation. It's hard - if not impossible - to implement anecdotal evidence, that also is 20+ years old (and might be a little biased ) . And on top of that, even if they could somehow get additional, not yet tabbed resources, those may either be classified and/or fall under ITAR restrictions.
Sure, they could guess, and err in favor of gameplay, but that would go against their standards. And would lead to a very slippery slope.
Either way, I have no way of knowing how the real deal worked, so I have to (and do!) trust in HB to give us the best representation of the AIM-54 as circumstances allow.