For the record, I never pored over any marketing materials for QC. I ordered it, made my own judgement, and kept it. It's no great mystery why - the reasons have been cited a million times - but the question keeps popping up as if it were rhetorical.
Non-rhetorical answers:
1. Between the captures, the models, and the cab sims, I personally think the QC sounds better than Helix or Kemper. (100% subjective and non-scientific, but a major contributor.)
2. Versus any other device with a comparable set of features, the QC has a much better form factor for my purposes (i.e. not on a massive stage every night.) 100% objective, measurable in pounds, inches, or metric if that's your bag.
3. The touchscreen, encoders, and UI overall are easier to use than the next most attractive option (Helix.) I
guess this is subjective since a lot of people like to nitpick about the QC UI. But I have QC and Helix products side by side, and I much prefer working with QC. To what extent this even matters will vary from customer to customer, but an intuitive UI is a big deal to me, personally. (Ergo however many months of my bitching about wack-a-mole capture menus before that was resolved. By far my biggest complaint from the onset, now resolved.)
4. Last but not least: this "lack of everything else". I think this has been substantially overstated right from the off. Totally a YMMV thing (i.e. depending on your need for very specific modulation and delay effects?) but I almost never find myself wanting for anything on my QC that isn't already there. (Exceptions are small and obscure, e.g. see above re: volume pedal curvatures.) Desktop editor? It sucks that they broke their promise, but I neither want nor need one. "Plugin support?" So I can get nickeled and dimed whenever NDSP drops a new variation on an effect? Thanks but no thanks. (If NDSP ever actually makes this happen, you'll start to see lightbulbs
finally going on over people's heads - the very same people who clamored for plugin support - when they realize they've been begging for the opportunity to be upsold into $3K QC's.)
If any of this is unclear... well, I'm as bored as you are.
Ask again and I'll answer again. As of this date and time, QC is still the unit I'd buy if I had to do it over again.