Well, my first reaction was "that's going to be a little too long" and Manny Ortiz seems to share that. 200mm on a crop body has you a little too far from the model. That said, the images are beautiful. The separation of subject and background is unparalleled and it looks a lot of fun, though I suspect it would shine in street photography in particular.
The X-T4 is impressive kit and as far as crop bodies go, I'd argue its best in class. While those 200mm portrait Ortiz takes are singular, when he switches to a wider prime, it certainly gives that more intimate feel. The autofocus and Eye AF appears to be slightly improved when compared to older models, but I'd have to use it myself it know for sure.
What do you make of the X-T4? Have you ever tried taking portraits with a 200mm prime on a crop body?