Well, they are exactly as mediocre as your digital filters. Except that e.g. Line 6 has a multiple of resources available to develop that stuff, compared to the audio companies you are referring to.
Besides, neither of those are where the art originates. The most advanced digitalisation tools, i.e. codecs, error correction, compression algorithms, signal processing and manipulation, QoS etc. are developed in telecoms, where you have tens of thousands of engineers figuring out how to preserve a signal over tens of thousands of miles and not where a handful of engineers are looking at the last three feet.
You are kind of proving my point here, by digital manipulation you can get close but never achieve the original.
About the guitar amps, does not seem to be your area, the cabinets play only a negligible role. All cheap MDF with 1-4 huge full range woofers in them and typically half or fully open to the back. No real science here.
Good, so you do concur that digital and analog sound different. That's the whole point.
I do not say Nord does not sound good, I do not say you cannot make them sound in different ways. I could imagine some may even prefer that sound. I am just saying, so far, you cannot make a digital simulation sound exactly as the original.
Then there is the dryness to digital amplification that just kills me. People talk about the liquid sound of tubes, so I might not be the only one who have noticed.
What comes to tubed electric guitar sound, I referred to the cathode follower principle earlier. That's the secret sauce. Also works in audio, my little EAR 834P Signature does that. While having other deficiencies, it gives me Jimi as close as possible to the original

.