All depends on the battery too, run a dinky 2ah battery and you won't get much out of it, 5ah makes them all work pretty good. IIRC according to many tests the dewalt 6ah is the best on high output tools.
Sockets matter too, some are better than others at delivering the torque to the bolt. Even the bolt length matters, a long bolt has more spring and gets torqued less, the ideal scenario is a nut on a stud, this sees the highest final torque.
I have run the 3/4" high output Milwaukee, its rated at 1,200 ft/lbs fastening torque, maybe it doesn't quite hit that but it's up there. For what we use it for its a huge cost saver, $600 impact vs $10k+ for a diesel driven compressor, air hoses, and air impact. We can throw a cordless impact away every 6 months and still be cheaper based on fuel savings alone.
True those are all factors, I have between 3-5 amp batteries. But you can feel the torque difference, I can hold the dewalt all day with one hand and it doesn't matter how hard it grabs it's nothing to hold, a 1" impact rated for 2000ft lbs if you don't have 2 hands on it solid it's getting away from you. Yea if the cordless will take them off it's way better option for the odd use. But if you're breaking off semi lugs all day even if the cordless can do it you'd kill the thing in a few weeks I bet, and you'd need 3-4 or the heat would eat them up in a day.