I am playing the eternal league these days, and I see the AI make the same mistakes over and over again. The mistakes are quite obvious, so hopefully easy to fix
The Set-Up to attack does not take into account that some of the AI players have block and some don't. However, when the turn starts, the AI suddenly does take the Block skill into account. This gives the following situation, where the blitz action is wasted on hitting the line of scrimmage with a Prestigore from the his right backfield (our left) with block, thus losing out on an important extra block:
Include the turn counter in the decision making. By turn 7 or 15, the AI should have at least one scoring threat, otherwise it can't score in turn 8 or 16. The AI ignores this fact and cages up too far away from the end zone to reach it in time.
The AI often move away from the opponent's ball carrier - and often even wasting the blitz doing so. Normally it won't be possible to blitz the carrier directly, but minimizing the amount of yards the opponent gains, blocking his way forwards, perhaps getting a tackle zone on the ball carrier, needs to be a part of the equation.
The AI will mark a prone player with multiple pieces. Marking a prone player with 4 players only makes sense if the AI is going to gang foul, but it is not. In the board evaluation, marking a prone player that is already marked must have decreased its board evaluation value.
PARAMETERISED BOARD EVALUATION
The best solution would be to have a "custom" AI mode where weight of each factor in the board evaluation is configurable. I am sure that the blood Bowl community can help with fine tuning it