Regarding the XT Live, I'm in much the same boat. I'm using a 750€ Yamaha guitar and a 350€ Roland Cube (RRP fifteen years ago - I bought them cheap second hand). I bought a Zoom G1Xon (80€), and have no trouble getting good tones from it, even on very different amps. All the presets are a very good starting point, and I only need to tweak them a bit to get them to sound what they are supposed to sound like. The problem with pedals like that though, with only an up and down footswitch, is that they need to be 100% pre-programmed for your set. So I got a second hand XT Live because it had more flexible footswitches. However, getting a decent tone out of it is much, much harder.
In my case the default presets were pretty much erased by a previous owner, and I can't reset the unit because then I'll lose the modelling packs they added. But using the Monkey software I have tried the default presets out one by one and didn't find anything close to what I was looking for. Further, nothing I've downloaded from the 'custom tone' site sounds anything like it is supposed to in the description either. For example, the Randy Rhoads preset I downloaded for the Zoom is beautiful without any tweaking. The Rhoads preset I downloaded for the XT Live sounds appalling; nothing like him at all, no matter how much I tweak it. Another thing is that I can make the guitar 'sing' and 'scream' very easily with the Zoom, whereas I can only describe the XT Live as 'stable' and 'flat'. For example, I can do pinched harmonics on it, but I'm left with the feeling that something was missing. With the Zoom I make a F*** yeah' face, and on the XT I tend to look over at my amp and make a 'WTF was that?' face.
I think the XT is much more sensitive to equipment, and much less versatile than the Zoom, and I find presets a waste of time. I'm sure the presets sounded good on someone else's guitar and amp, but they don't translate well. Especially the way the cabs interact with the Stomp effects. I can get a half-decent tone using an amp/cab model, but then the Stomp effects just destroy it.
I also find some of the default settings for the effects completely baffling. As you say, everytime you turn the tweak button, you don't know whether you're going to get your head blasted off. And some of the default settings just don't make any sense at all - as if they were set by a Line6 tech who didn't actually play guitar. It is really, really annoying that we can't save over the default settings of the effects. It should just remember the last user setting, and I think this is the biggest flaw of the unit.
I've had the XT Live for several weeks, but I've only had a few hours to mess around on it during that time. The main problem I have at the moment is that I can't play loud in my apartment. So when I set-up tones at low volume that sound OK, when I take them to rehearsal, they sound completely different (and usually really horrible). I'm going to try to find a way of spending a few hours alone in our rehearsal space, creating tones from scratch at high volume, before I give up. I only paid 100€ for my unit, so it's not a disaster if I end up getting rid of it.
But I still have hope that I can find one tone that I like which will sound good throughout the whole clean, crunch, distorted, chorus/phaser, and wah range of effects. I mean, professional musicians used this unit for gigging back in the day, so it must be possible to get a decent tone out of it. I should have more time over Xmas to play with it, and will post back if I have a breakthrough or some kind of epiphany. I don't think many of these older modelling units do Metal very well though, so I may have more luck than you. This guy seems to know what he's doing, so I guess this is as good as the Metal tones get. Sounds OK, but nothing special.