Just don’t touch the heroes ever. The mission is still manageable without the atk boost. If you struggle in the final part: Send Ele Archer/Siege Ele around to the left side and take down center/left Castle and Wonder, and 3 starting Trebs with some guards for the right Castle (use command to heal them, you can make additional trebs after meeting with the general). The rest at the middle to distract their main force. Try to have the battle near green’s base so they don’t have time to come back to save the center Castle.
At least try to take the Wonder, then fall back and turtle until you mass Ele Archer and steamroll.