Thanks for the welcome anyway.
I haven't tried playing against 3 allied Magic opponents yet. Must be quite a challenge but I'll have a go.
I've found the following tactics to be successful for an early attack:
No time must be lost in creating the attacking units.
The 5 Battlemages, and 2 Daemons must be brought to the enemy Base at the same time but the Summoner will arrive a little later. After positioning the Battlemages, the enemy Archers and Swordsmen will always try to kill the 2 Daemons so by moving them around with the mouse, enemy fire is not directed at the Battlemages. After the initial enemy Archers and Swordsmen have been eliminated, the 1 or 2 surviving Daemons can be positioned at the corner of a Farm farthest from the enemy Defence Tower and contribute to demolishing it.
When the allied Tech enemy comes to the rescue, it is necessary to interrupt the attack against the buildings and deal with the approaching Archers and Swordsmen. If the enemy Castle is not destroyed due to the arrival of enemy reinforcements, one must retreat and draw them towards the approaching Magic reinforcements. After that one may return to attack either the first enemy base with the help of the ally or attack the other AI Tech Base which will be equally vulnerable.
The Summoner is very useful for destroying the buildings but very vulnerable to enemy fire so care must be taken to protect her.
After demolishing the Castle, one can safely retreat to the Allied Magic Base to help defend against the impending attack but, if possible, it is a good idea to destroy the entire base, specially the Defence Tower.
Fire from the Defence Tower is always directed at one Battlemage or Daemon at a time so by moving the attacked unit around with the mouse, the other Battlemages can destroy the Tower undisturbed. The Golem can be attacked in the same way.
Using these tactics, with good play, the game is already won against 2 ultra AI Tech opponents after the fall of the first enemy Castle. It is very easy on some maps to go on to attack the second enemy base but more difficult on others like the Swamp of Sorrow where the enemy counterattack can be stronger and it is possible to lose.