Congrats on the truck and welcome to HDRams.
Sorry you got caught up in it, but it's pretty well known that the Cummins 2500 trucks don't have a large payload to begin with and you add on the full boat Limited/longhorn trim and there goes more payload. The Cummins is 600-700 lbs heavier than the Hemi. If you have an HO (only available on 3500), the whole package - engine/trans/xfr case is around 1,000lb more.
The D-max probably also has the larger GVWR that GM offers. Not one single difference in the trucks for the 10K GVWR vs 11400(?) GVWR, it's just a door tag. Ram has been slow to offer the same.
Compare the 3500 trucks and they're too close to call. My 2020 Limited CCLB HO is 3700 payload and 25K towing. The HO Cummins is also rated to tow more than the Dmax.
More importantly, what are you towing and is the 1900 payload an issue? You can always add airlift bags for more capacity (but that doesn't change the sticker). The truck is more than capable of handling it.