Think you might want to check (and cite) those numbers again. I think you've confused launch mass with cargo mass.
- Dragon delivers 2300 lbs (1045 kg) cargo to ISS.
- Cygnus delivers 2000 kg (standard) or 2700 kg (enhanced) to ISS.
The vehicles serve two very different purposes upon reentry. Dragon brings back garbage and recoverable cargo, Cygnus just takes out the trash. That's one of the reasons that Cyngus carries a much greater payload to the ISS. So if you are going to do any kind of back-of-the-envelope calculation about which one is a better value for NASA, then you have to include the value of bringing the wanted & unwanted cargo back versus disposal. Your argument reminds me of the old "which is better, Mac or PC" arguments we used to have in the 20th Century. The answer is "two players are always better than one." Now, how can we extend that analogy to SLS
... "which is better, Mac, PC, or IBM/370 running MVS?" Hmm, IBM/370 may still be considered a lightweight compared to SLS...
And what exactly do you mean by "stuck in orbit?" A functioning space vehicle that maneuvers and allows another visiting vehicle (Soyuz) to rendezvous, before making its own approach, hardly sounds "stuck."