From a campaign perspectrive?
We get to pick what our fictional commanders send on fictional missions for fictional generals in fictional operations. That's fine for the bar of historical platitudes, apparently.
We can choose to request planes that never landed at X airfield or did Y raid over Z location, and that's fine for desired standard of historical accuracy. We can ship more of a vehicle than existed, never mind served. We can mix and match gear and manpower and hardware and send it to places where literally nobody foguht for brutal slug fests with enormous axis or allied armies.
But a commander requests a vehicle that's sat in the mainland UK to be shipped to the front line, and suddenly that's where the line in the sand emerges... that's the step too far. Now it's a problem?
You're already accepting that none of the battles you do in the campaign are true to reality, using hardware and material and locations that's ahisoirical but available to the army in question.
The BP... is ahistorical, but available to the army in question.
I think the point people are trying to make is that there's a difference between historical realism in terms of aesthetics and in terms gameplay, and that you can have the former without the later.
CoH isn't a "realistic" game in terms of gameplay; it's based on reality, sure - but it's in no way a simulation. Units are "stylized" to fit the mechanics (ranges are reduced, HP and armor is increased, etc.), but they do remain true to their source material; the Tiger has a lot of HP/Armor, a big cannon, and is slow and expensive. The T-34 is pretty cheap, but not that great, etc. When you look at those units, though, you can say "yea, that's pretty much a [Tiger/T-34/etc.]", and more importantly, the interaction between
the units makes sense. The JT doesn't tend to bounce off mediums, air-attacks do a ton
of damage to slow/immobilized heavies, and so on.
When you look at CoH1 and CoH2, every single unit and ability is at least plausible. Railway artillery existed and was used - probably not on the battlefield - but if the situation arose there's no reason it couldn't have. The same can be said of the "tactical V1"; it doesn't make a lot of sense historically, but V1s were real, and could be aimed to some degree. There's nothing (at least that I can think of) that immediately jumps out as 'impossible' in either games; there's no Maus or E100, Panther 2, T28/T95 (US), IS3, Tortoise, or any other "slightly too late" late-war or 'never produced paper prototype' in the game.
The BP however, is exactly that; there's simply no reality in which it could've appeared in Italy. The design started
in 1943 and the first 6 prototypes
were delivered in May 1945 - after the war ended. No commander, no matter how persuasive or powerful, could have summoned these vehicles to Italy, and no incredible chain of events or coincidences could resulted in them appearing, because they simply didn't exist - there was nothing to send.
It opens up the door to other units of this type, which some people (myself included) just don't want.
What's stranger is that most of this could be avoided by simply switching the model to CoH2's "Comet". While it didn't historically serve in Italy, it did first see action in December 1944 in Belgium, during which the Italian campaign was still ongoing. The "ahistorical, but available to the army" idea would actually work with it.