IMHO the X and the V4 have different qualities. The V4 is stunning. The X is stunning.
The X feels like a heavy and sturdy workhorse, but its button is extremely comfortable and has a featherlight operation, with an ingeniously hidden locking mechanism. What I also like is that it rests so perfectly in my hand (especially in 18350 mode and with a Spheroid on it) and that I can also press the button with the palm of my hand or in any other position. The X button is also very tactile, it gives you clear feedback when it activates, which is a great quality.
The v4 seems (I don't have one, not yet) more subtle with a very small button
throw and refined looks. I think its design is even more sophisticated than the previous PAPS versions. Like with the X, the button and locking mechanism of the v4 can not get stuck or loose. Unlike the X, it provides a perfect fit with the Heron (and hopefully an even more seamless fit with the upcoming Heron v2).
IMHO the X and the v4 cannot be compared in terms of better or worse. You just need both of them