When you buy the Pro-version of Capture One, it also has support for tethered shooting with the X-T2. Make sure you have a very good micro-B cable since Fujifilm cameras are very susceptible to cable quality and length. I can recommend the Tethertools cables.
Aren't you accidentally looking at the embedded previews in the raw files? They have a reduced resolution. When you look in-camera you best view at the processed jpegs when you shoot raw+jpeg. Some users separate raw+jpeg across the two card slots and review only slot 2 (the processed jpegs). When you assess the images on the computer, make sure that the full raw file is loaded instead of the preview.
Another suggestion is to look at focusing. Many people coming from a DSLR struggle a bit at first with mirrorless focusing. Make sure you have the right focus mode and shift the focus point to the desired location (joystick) rather than using the focus + recompose method.
Finally and in all honesty, no matter how good the X-T3 is, there's still a difference with full-frame. Esp. in lower light situations. I've used the 5D in various versions and it is a 'beast' of a camera. Depending on which 35 + 85 you've used, it was until recently the go-to camera for most professionals and for a good reason.