Don't really count a AR as a build, since it more of an assembly only really.

FAL's are more of a build than assembly, since you need to first get the barrel to index correctly to the receiver by facing the barrel shoulder, then you need to adjust the bolt lock up/ head space via the correct size cross pin that is pressed in.

Same goes for HK with a completed receiver, since here you only need to press the barrel in the extension correctly to achieve the correct free gap between the bolt to carrier, before you final drill and cross pin the barrel into trunnion. Same goes for a AK on a completed milled receiver as well.

From there, you get into a lot of jig and welding to first complete a receiver from a flat, then your back to installing the barrel to the trunnion/ riviting on a AKM type receiver.  Or you are machining a new receiver on parts kits that the milled receiver has be dewalted that no one offers a completed milled receiver instead.

As for truth being told with the drying up of imported dewalt kits/ the prices way too high to start with, and the lack of ability to get a decent new completed receiver (Imbel receivers on the FALs, and FMP completed receivers on the HK's), then you back to just assembling AR's since you can get a receiver on the less expensive side, and part together complete rig for less than $500 isntead (about $600 on a 9mm rig, and about $800 on a 308 rig).   Hell use to be a time that you could get pistol kits on the cheap (sigs and such) to complete them on 80% receivers, but now a days, buy the time you get the parts and 80% receiver, your already over the cost of just picking up a factory refurbished completed pistol instead (think sig CPO pistols).