Yes, it is completely useless.
The AI works by scripts that set certain hexes as targets at certain points in time.
Or in other words, it relies on the author of the script being able to predict the most plausible cause of action that the player will take, and program the script accordingly.
Which is fine(-ish) for shorter scenarios where the options are limited, but completely bonkers with longer scenarios.
Imagine having the Panzer Lehr arrive at Normandy after a week of fighting.
With no knowledge whatsoever of how the battle has progressed thus far, where would you direct the AI to send it?
The AI is by far the biggest weakness of the PzC series.
The only way to play the longer scenarios with any degree of satisfaction is to either do PBEM, or do hot-seat and play yourself, as it were.
Like yourself, I prefer solo-play allowing me to come and go as I please.
So I do hot-seat campaigns, and I've found a reasonably satisfactory way to do it.
For each day, use notepad and write down general orders for each major formation (divisions on the Western front, probably Corps in the East) , and then do your utmost to stick to those orders.
Granted, it does take a certain amount of schizophrenia and it's a bit like getting a kiss from your sister, but it does sorta work.
Certainly better than playing the AI. :)