The original springs were progressive wound. That means the first inch will deflect with less load than the rest of the spring. So the small bumps are taken up easily while it doesn't affect the load carrying ability much. The lowering springs are not typically, or ever, progress wound. So if you go the typical lowering route with shorter coils and spindles your truck will ride rougher than it would have been stock. The none-progressive springs keep the trucks from bottoming out on the rubber bumpers as easily as it would otherwise. You could conceivable cut the side of the coil without the progressive wind and not affect the ride but you will likely bottom out easier. Most just purchase the springs.
If you have a GMC or lief spring options truck you could flip the axle to the top and not affect the ride much.
I can't speak for air bags. Most say the ride is superior to springs. Obviously when you compress the bags the pressure goes up and they become self regulating so to speak. And you can pick your ride height. The alignment has to be a compromise for the same reason, height changes.
I believe the difference comes down to cost. Air ride is going to cost more and to buy and install. Especially if you go with the ride height sensors. Would love to here from the guys that have installed the air ride system and give it a cost comparison. I have seen ads for the complete front suspension with lowering spindles And a narrowed track width for driving and turning low. Wheel position has been moved forward 1" to center the wheel in the wheel opening. Upgraded steering to power rack and pinion. The price is $4500.00. Still no lines, controls or compressor and it includes nothing for the rear. Costs go up quickly. I see these on higher end builds for a reason.
A lower cost option on Amazon here;
$1,249.00
https://www.amazon.com/airmaxxx-Susp.../dp/B01MR1CSU1
One review lists the customer service as crap. And goes into detail. The only other list it as Works good."
Cheers