I’ve done quite a bit of capturing on Stadium as well as Tonex, QC, Kemper, NAM, and Headrush. The majority of it has been amp+cab, mics, preamps, etc, but I’ve done a good bit of direct amp only capturing as well.
Personally, for all the above platforms, I far prefer amp and cab captures. They always sound better to me than a direct capture and an IR, even when the amp is set exactly the same and the IR is shot with the exact same cab/mics/preamps/EQ, etc. There just seems to be more magic in the full amp+cab version.
When it comes to direct captures, though, having a real cab connected makes a pretty big difference, IMO. I’ve done captures of amps connected to load boxes only with Ox, Captor X, and Reload II. To me they all perform similarly, but none of the captures I’ve made connected only to load boxes sound or react as good as when the amp is connected to a cab.
These days I make direct captures with the amp connected to a cab and a Neve RNDI between the amp/cab to get the direct signal. On Stadium when I’ve made clones like this, the direct clone + IR sounds really close to the amp+cab clones I’ve made at the same settings, but again, I prefer the amp+cab clones.
So long story short, yeah - I believe making amp only clones with the cab connected makes a pretty big difference. I understand it’s difficult to do a lot of capturing like this because of the volume. I’m lucky that I’ve got a separate cab room that I can pretty much blast 100w heads into 4x12 cabs at will