The problem with that argument is that many players will still feel robbed if they can't actually finish the campaign, and get quite frustrated - I have plenty of games that I've abandoned because the campaign put up a wall to me (I was never able to even complete the first mission in Men of War: Red Tide, so that was money well spent
)! I just accepted I wouldn't win with a sufficient margin, knowing that I could play the scenarios individually at a later date, but lots of people seem intent to bang their head against that mission until they win. I see the problem being one of difficulty management; generally games have a difficulty system (easy, medium, hard) but UoC uses a degree-of-victory system (standard victory, DV, BV) which equates to the same thing (If I want an easy game, I aim for a standard victory; if I want a hard game, I aim for a brilliant victory). When playing separate UoC scenarios, the player has full control over the difficulty, but in the campaign everyone
is forced to play on easy/medium/hard depending on the scenario, if they wish to progress. This approach is a bit punishing to those who wish to play an easy or medium game, because they can only feel that they have failed in the campaign as it is set up, when they have actually probably done pretty well.
The argument that aspects of the campaign are non-historical doesn't really give the excuse for making it prohibitively difficult at particular points. It would have made more sense to have the campaign be historical and add some non-historical scenarios to be played separately or just to say that there is a longer gap between steps in the campaign so that the timeline made sense.