You can't say that guerrilla tactics are conventional. Guerilla warfare by definition is unconventional and irregular fighting. My question at this point is where are you finding information about them fighting open battles? Every time they come out in the open, they are bombed into oblivion by all the air forces targeting them. Their only asset is to remain unknown and not easily identifiable, otherwise they will be obliterated by the superior militaries targeting them. I can't imagine they have "uniforms," because if we could easily identify who is ISIS from who is a regular civilian, we wouldn't have such a hard time engaging them. There are stories of them dressing in Kurish uniforms to infiltrate an area undetected before they start fighting, but as soon as they come up against superior forces, they disintegrate out of necessity. That's not conventional fighting at all, even if it's the norm for insurgencies (which is nothing new, that's how America colonials were effective against the militarily superior British in the Revolutionary War).
I see what your saying. In the past guerrilla warfare was characterized as special warfare or even unconventional warfare. But modern warfare tends to draw the line at who they targeting and if they fight in uniform. Special forces are our equivalent irregular forces. DAESH forces do wear uniforms and primarily target military targets. They also practice terror by distributing horrifying videos to scare the population. Although they have now stopped this practice and no longer will show decapitations.
But they do fight open battles from fixed positions in uniform. They use artillery, anti-air missiles, light and heavy armor, etc. These things are even beyond guerrilla fighting Their forces are arguably the most competent in the regional fighting. They know how to hide and when to move in a way that we can do little about.
For example there is a lot of talk about air-strikes. Well, that window has closed a lot. 75% of the air sorties now return without dropping any ordinance. We really have few actionable targets. Even though you can see them walking around everywhere, we can't hit most of them because they are in civilian areas or the targets are not cost effective. We would go broke trying to kill all 100,000 of them with $10,000 hellfire missiles.
The time has now come for ground forces to fight, but it is not clear who that will be. The YPG is often seen as the group who will fight. However they are only interested in defending the country of Kurdistan, and frankly the Peshmerga are overrated. The next most effective force is Iran. However they are interested in controlling Iraqi territory and spreading their influence. That leaves the U.S. and the Iraqi army. I don't see how that is going to work. The U.S. is not going to commit the hundreds of thousands of ground forces needed to win and the Iraqis don't have the fighters. Forget about training them, we have been doing that for like 11 years and have about 2600 reliable fighters. At that rate it will take a century. I really don't see how we are going to do this.
"Unconventional and irregular" fighting is the definition. Conventional warfare is still considered to be fought by "official" armies furnished by nation-states (official meaning the army is a proxy or extension of the political rulers), where a formal surrender or treaty is signed upon the defeat of one side. Conventional warfare doesn't really happen anymore because nation states rarely go to war anymore for many different reasons, not least of which is there is no economic reason to, but that doesn't mean the norm of guerrilla warfare by insurgents is now "conventional" warfare. Guerrilla warfare by default is unconventional because there usually is no nation-state the fighters represent, or at least no traditionally recognized nation-state. Perhaps that is all a designation of guerrilla warfare has ever meant, as opposed to two nations that formally agree they are at war and will fight until one surrenders. That's how I take "traditional" war to function, the formality of it really.
The things you described Daesh doing are certainly more conventional (use of artillery, light/heavy armor, uniforms in battle), but do you have any reports of this? I haven't seen any reports of them using these tactics recently, and only vaguely remember ever seeing any. My understanding of the situation is that these tactics have largely been abandoned because it makes them too easy to target by air.
I agree with your third paragraph. Daesh is not defeatable at this time without ground forces, and the ground force by proxy has been a disaster. That still doesn't lead me to believe our ground forces should be committed.
