Every race should be played differently (like undead in original). We though the daemons are a real threat in lore, if only one rift got opened and created such chaos. A rush to close it would be necessary to defeat them. Therefore, their units are produced fast (less than 10 seconds) from a single building (Pit). Summoners, a.k.a. worshipers, are the only link between the daemon plane of existence and etheria. It is why they are produced at level 1. They can now Blink, which is a known summoning teleportation spell. In long matches, summoners can be hoarded safely in the base to summon daemons. A daemon side with its summoners killed is a loosing side. When the hero uses its Racial Synergy Bonus, beautiful succubus spawn around the hero (number depends on time passed - so it is best to use it as late as possible or in an emergency) who provide valuable souls for the daemon army, and souls = mana = strong army.
And now my personal opinion: After playing a few matches with and more frequently against the daemon race, I have concluded that it is the most unpredicted side of all. It is the battle-turnover you are hoping for/against. Just one pit built near the enemy base can easily create conditions for a (or more) surprise attacks. You can provoke the enemy to leave its base defenseless (especially when fighting another human player), then pillage everything. Late game you can, of course, summon daemons and imps for free. Creating ugly thunder storms gives an enormous advantage most of the time (beware the barbarians though). And let's be honest, blinking is the most useful escape/ explore spell in the game, now that it is targetable.