You might be right. Not sure how you know it will sound great. The sounds in the Line6 vid were meh at best.
Because the videos in the Line6 video either:
a) Used the internal Powercab Speaker models which are downright terrible (based on experience with the older Powercab)
b) OR they used an IR on top of the speaker (which is now a guitar speaker). This is unlike Kemper Kab / Kone where they do complex convolutions.
They key here though is that this unit has a guitar speaker. That is the big differentiator because it brings big improvement in tonality and feel compared to FRFR.
Yes, this is just one guitar speaker (given that it's a fixed physical unit) but that's all you need most times when you actually get down to playing. I'm sure the speaker was very carefully chosen.