I've never seen amp/cab modelling falsely represented by anybody. Of course it's largely done through things like EQ and compression. It's all about how they handle certain frequencies.I'm not saying you can't get a good sound with modelling and I'm not saying it shouldn't replace your SVT as long as you're happy with it. I also use MultiFX through a power amp so I'm certainly a proponent of what ZOOM and Line 6 is doing.
I'm saying that modelling is falsely represented and that you could get the exact same sound using EQ and compression in the MF unit. The modelling essentially acts as a preset, but often lacks the fine tuning you can then do with your own EQ/comp settings. It fools the consumer by offering a false representation of what it's doing.
Case in point, modelling a SVT amp/cab through one class D and speaker is going to sound different from another set of class D and speaker. More than likely their modelling was designed and tested on studio monitors, so what the end user is getting running a sim through any given combination of real amp/cabs is a crap shoot.
So for example, using a modelled SVT amp/cab, through an ART preamp, through a Mesa class D, into a Ampeg 410 is going to sound completely different than using that same modelled SVT amp/cab through an Aguilar tone hammer into a Hartke 410. So yes, it is smoke and mirrors because what does the modelled SVT really "sound" like?
It's a gimmick. Personally I don't care if a comp is called "Ross" or "Grey" or "ZOOM comp #2" as long as it sounds good but expecting the same results as a real Ross is a gimmick.
I'm not sure why you're including amp sims in this though. Your rant doesn't apply at all to any amp sim I've used. It's far more than just EQ and compression, and there's plenty of knob tweaking and fine tuning to do. Cab sims tend to be more "pick one and that's it" with no tweaking.
As for your examples, yes, of course they use studio monitors...something FRFR, to avoid coloring the sound. And they heavily recommend that you use FRFR speakers. Otherwise, you're essentially nullifying (or at least modifying) the cab modeling. That's rather obvious, isn't it? "Uh, yeah, Line 6, I've got a complaint...when I play your Hiwatt model through my Fender amp, it doesn't sound like a Hiwatt any more." It's basically like complaining that stacking a Muff after a Darkglass pedal changed your tone.
You get a different sound from headphones than you get from studio monitors than you get from a guitar amp than you get from a bass amp than you get from a PA than you get from going direct to FOH. This is not a secret, and it's not unique to modeling.
If you're really going to be consistent, you have to say nothing really has a sound. How can we say what a Muff really sounds like? It's very dependent on what bass you use, how you set the bass's tone or EQ, what amp you're running it through and how you tweak that EQ, and all sorts of other things including playing style and the rest of the signal chain. So it must be "smoke and mirrors because what does the Muff really sound like?!?!" Hell, what does a P-Bass sound like? The sound changes drastically depending on what amp you use and how you tweak the knobs etc and so on. That's an inane line of reasoning.