I don't think the Core sounds better, especially with stock cabs. The stock cabs on the Boss units really lend towards a mid forward, boxy, nasally tone.
Here's a video where the Boss amp modeling goes into the UAD Ox Stomp and IMO sounds really good:
Honestly I've been thinking of trying out that Ox Stomp to see how it compares to other cabs. It generally sounds quite nice.
Anyways, with some tinkering and the right IR's the Boss can sound pretty good, but it's got a more limited sweet spot of good sounds. The HX can sometimes sound better with different settings more like an actual amp in some cases. Even if the modeling tech is older and maybe not as high fidelity as newer stuff.
I will say the IR-2 which I think uses the same tech can sound quite good depending on the amp model. Sometimes there's more of a midrange cut which is pleasing, less saggy and mushy compared to some amp models in other units. Other times it can sound and feel like running into a distortion pedal through an EQ pedal and into the board. Very harsh direct and "digital". Generally the cleaner amps up through crunch and the X amps IMO are pretty good. I don't like most of the other high gain amps though. You also have to watch out for the cab that's paired up with the amp model too...sometimes that can wreck the sound.
A lot too has been made of the very low latency. This became a big deal a few years ago when Leo Gibson started testing latency of all units. It is quite impressive, and maybe for some people that makes a difference. I don't know if I could tell much of a difference when I had it.
One thing that is obvious to me is that the Boss generally sounds a bit bright when running signal through it, it could be the converters being so high fidelity but it seems there's a bit of EQ lift. Other units like Line 6 may be slightly dark.