I have an 11,000# loaded 5th wheel and with everything loaded up (hitch, people, 5th attached, etc.) I have about 3000# added.... most of which is in the bed, of course. I have Firestone 5000 airbags are like them. Could I live without them? Sure. The truck actually sags very little under that weight. The coil springs with these trucks are very stout and capable. The main benefit to the bags is they just stiffen up the "hinge" between truck and trailer and help control the rhythmic bouncing that can happen over bumps.
As for RAWR, I think the change from 6500# to 6000# was around 2018 but can't remember for sure. Of course, the door sticker is always the best way to know. I have a suspicion that the rear axle on the older 2500s might even really be rated for 7000# as it was the same one used on the 3500 SRW during those years. I got into a debate on a message board once and someone posted a bunch of part numbers but only the newer years (2018 onward) showed different ones from 2500 and 3500SRW. I didn't ever research it more since it doesn't matter to me but if someone wants to geek out on part #s you might be able to figure it out.
The whole payload vs. axle weight argument has and will go on until the end of time. I run right at or a 100ish pounds over payload (3000# - Hemi with 7000# unloaded weight) but am comfortably under axle weights. Tires are rated at 7200# total and axle is 6500# (maybe 7000#). The most I've ever scaled my rear axle when totally loaded is 5800#. I'd have no problem doing the same with a Cummins.
