The thing is, the enemy's troops might be positioned in such a way that we won't have the opportunity to deploy our troops in a tight formation. It's unlikely that the bonus for a single stack will even reach 5. Again, if we're going on the offensive, someone will still remain in the rear (these are archers and possibly someone for cover), which also won't provide much of a bonus. When defending, and even with tactics, you can perfectly position your troops so that the bonuses are noticeable, but what's the point if they can be scattered during the battle? After all, the stacks won't stay in their starting positions all the time. Unless it's against a barbarian, and even then, he can only attack after using his war cry. He casts "war cry" (+10 to attack and +1 to speed at level 20), and all the efforts with formations go down the drain. And if there are no obvious attackers and defenders on the battlefield, the troops will be randomly scattered, and it's quite a difficult task to organize a formation effectively without hindering attacks on key enemy stacks.

I disagree with the summoning part... The dwarves' troops are among the best in the game in terms of efficiency; with approximately the same ratio of troops, the dwarves are stronger than many, and extra reinforcements won't hurt, especially if you summon troops wisely, they won't get in the way. I don't find the Ring of Exile very often. You also need to upgrade Exorcism and take Chaos. This setup is only possible if you're going for a solo campaign. It's not profitable to sit in defense because the demon will overwhelm you with darkness, and you won't be able to use light effectively; the imps won't let you. Not to mention the demon's powerful ballista, which will also do a lot of damage.