Line 6's past products are soooo terrible that they've been immortalized on entire albums from Devin Townsend, Animals as Leaders, Meshuggah, Twelve Foot Ninja, Monuments, and so on and so forth. A kazillion other bands use them live to this day to reliably and ably gig. That's terrible?
Well what you say definitely has merit, many of those guys (specifically Devin Townsend, Animals as Leaders, and Meshuggah) all moved on to the Axe-FX after it caught on. Twelve Foot Ninja and Monuments still use Pod though. I know Joey uses it, but honestly, that's his sound now. And you can also bring up Andrew Wade, but from what I know, he only uses it when it's requested and admitted that it's the worst sounding sim technology these days (Pod Farm).
Remember that this is a recording forum, so in most cases, we talk in context of the studio and not live. Honestly, I've seen guys use Marshall Mode Four's with a MG cabinet and tbh, no one really notices live because half the time you are running through a shit PA with an even shittier engineer anyway, not too mention, everyone's drunk and just there for a good time. It's not like the standards are very high live IMO.
A trend I often see is that many of these djent/progressive bands (like Periphery as well) who started out with the x3 moved on after the Axe-FX came out because ultimately the Pod series became stagnant, outdated, and honestly, lack luster. At the time it was decent, but to say that Line 6 products aren't terrible (in the context of today, which is what most people are obviously considering when they say Line 6 is awful) today when there are much superior options IMO (such as Recabinet, TSE) or Kemper/Axe-FX, I just can't see it.
I never used a Pod HD, but from the clips I've heard it just doesn't measure up to the competing options. Obviously it's cheaper, but if we are talking purely about what sounds good (or terrible) and what doesn't, then it obviously gets shit on by Kemper/Axe-FX and I'd even argue by TSE/Recabinet which are both cheaper than the Pod HD. Now, can the Pod HD be usable? I'd argue yes, but is it the best option for price/performance? I'd argue no.
Honestly in the end, when I used to use Pod Farm for my tracks like four years ago I was able to get usable sounds, but then when I started using other alternatives, notably Recabinet and TSE I just found that I got results quicker, which is what turns me off Line 6 products. This became even more pronounced when I started borrowing my friends Kemper. Especially with Pod Farm, I always had to cut odd frequencies, specifically in the highs, to make it sit right whereas TSE x50 just sat right very quickly.
Like I said though, I'd like to hear the Helix before blatantly writing it off because it says Line 6. I'd love to be surprised.