Is it just the HX Stomp though?
I play in a three-piece metal band, both the guitarist and myself played on Helixes. At our first shows, people regarded our sound as 'thin'. After (another) hundred hours of adjusting tones we even obtained 'great tones' kind of feedback.
However, no matter what I did, I felt the sound to always be somehow...unsatisfying. I completely agree and understand those who say there's something wrong with it, something you can't 'really put your finger on it'. And don't get me wrong, I'm not some valve purist, nor am I a great audiophile, tone guru or audio engineer. Quite the contrary, actually - I am not very picky. All I wanted was a "normal" sound, which I heard whenever I connected to a guitar or bass amp, a simple, normal and yet satisfying sound that somehow I never managed to obtain with the Helix.
I spent hundreds of hours trying various effect combinations and setups, online presets and IR's. Every time I spent more than 20-30 minutes setting up an effect, my ears would get tired and I started perceiving the preset as being 'good'. Next day at rehearsals, my ears would bleed with disappointment and desperation, as it always seemed to me as if the effect is some sort of joke, a parody of what I thought I obtained the previous day setting up the preset.
What I found strange was that the the more unnatural and illogical the preset, the better it seemed to sound. Sometimes placing a cab before the amp or having a split signal from the amp that bypasses the cab and goes in the output through a distortion pedal seemed to actually make a desired effect. The simple presets sounded rubbish. And it was those that I wanted to sound good - I didn't want any intricate signal chains. Just a simple, plain pedal > amp > cab thing. But something always seemed to be off...
My rehearsal room setup was guitar/bass > Helix LT > mixer > PA. And that was the problem.
Just because you can simulate the sound of an Ampeg or whatever, it doesn't mean it will sound like an Ampeg. If you don't have a high end mixer/PA, it will absolutely, and without any doubt, not sound like one (maybe even sound just plain bad, like it happened to me). So no, your guitar will not sound as if you actually own a Mesa Boogie, if you have a major bottleneck. It is not 'ignorable'. It is not 'secondary'. If you think you're getting a Helix and you're gonna sound great no matter what, then you might as well buy some subscriptions to 'how to play guitar like a pro in 30 days' programs. And in the next month maybe 'become a programmer' and 'build muscle like a bodybuilder'. Hope I'm making myself clear - the Helix alone is not a shortcut, not in the way that it seems to be when you put it into words such as 'it simulates a darkglass connected to a valve markbass and a 8 x 10 cab'. The tone might sound great at some venues (or, of course, open-air festivals where they have high-end equipment), but the sound might vary greatly between the rehearsal room and live sound.
I had times when on certain mixers and PA's I was surprised on how well it sounds, and times when I just wanted to smash it with a blunt object. I made the mistake of thinking that if I buy this rather expensive piece of equipment, I could get away with it but I learned the hard way this is not the case. I found it to be too much of a struggle for me, and that it implied other investments to make it work the way it makes you believe it should work.
To me, it was too much of a headache. But as a conclusion, to anyone struggling with the tone and having the same experience I do, consider the other equipment in the signal chain - are they of equal or higher value, worth thousands, or are they cheap stuff bottlenecking, giving you nightmares? Maybe this is 'that thing on which you can't really put your finger on' - the hope that a thousand dollars (or whatever version of Helix we're talking about) piece of equipment, will sound as good as a $5000 setup.
I think that no one will ever buy a real amp and cab again if somehow this promise (if I may) of "simulating other amps and cabs" would work as intended, without requiring other high-end investments. I hope that day comes.