I would say the main difference that kind of dictates everything is the treble difference here. Because the XV is darker in key spots around 5 and 10 kHz, the treble response sounds a lot smoother and more relaxed relative to the FT1 Pro. What this also means is that the midrange and bass sound louder relative to the treble, so the Edition XV is both a more midrange-focused headphone than the FT1 Pro, as well as one with a more compelling, full bass presentation thanks to the lower and center midrange being relatively much more pushed. I don’t find the FT1 Pro particularly impressive in any subjective aspect but in basically all of them I hear XV to be a meaningful improvement (but again, this could very well be down to how much better its treble works on my head vs. other headphones)
Hope that helps!