I love Xtol, and was my prized developer of choice since it was released, it works wonderfully with Ilford HP5 which is my primary film. I have developed with D-76, Microdol-X, and Rodinal, and found Xtol suits my tastes perfectly. On some level I agree what you mean about muddy and flat but for me it is with Ilford Delta 400.
However, after some bad batches of the 1L bags (a late notice press release from Kodak, and two contracts down the drain) my confidence was shaken. That is all it takes for me to move on. I have since switched to Pyro PMK 1:2:100 with all my film. I shoot 35mm,120,4x5, and 5x7, with Ilford HP5, Detla 400, HP4, Adox 100, and Rollie 25. And have excellent responses, including scans, but having said that, I print first to FB paper (analogue photoshop) then scan. Good luck finding your combination!