The relative lack of endoskeleton, yeah, that's true enough. A casual fan will want endoskeleton on their Terminator figure. Having said that I did replace the jackets and in some cases the pants on my DX13s, I personally wasn't happy with the tailoring on the jackets - they overcompensated for the MMS117 problem where the front would be too wide open and this resulted in the front being too closed on the DX13 jackets, therefore obscuring the chest battle-damage more than one would like. So I went with MMS117 jackets for most of mine, that was expensive though. Thus for me both figures require clothes changes.
Having said that I don't think most people care that much about something like that and you're right that the presence of endoskeleton parts will be more important - therefore DX13 wins, out of the box.