Combat is a second thought in regards to design as it´s very lacking. You have "a lot" of stuff to learn but only on the player side. You don´t need to learn about enemy behaviour, special capabilities or anything, that´s why I say that the system is complex but not deep or balanced. Look at it this way: In Doom you have a much more simpler system, however adding different types of enemies to an encounter can change drastically how you approach it. You have to prioritize what enemies to kill first, what weapons to use to be more effective, to rush or stay away...all these decissions are related to each other. This system has depth. Now look at any encounter in Xenoblade X. Adding an enemy only poses one question: Is the enemy too high level? If so, you flee or you die. If not you just play the encounter as you would against one enemy, repeating your strategy-cycle until all enemies are dead. This is the only decission you ever need to take in any encounter in the game.
Have you ever played Dark Souls? All the combat flow revolves around learning the enemy´s behaviour and choosing the right moment to attack, block, roll or parry. If you focus on your inputs and disregard the enemy even a Hollow in the Undead Burg can kill your level 120 knight. In Xenoblade X you don´t have any actions to react to what the enemy is doing. The fact that there are overpowered builds where the enemy becomes even more irrelevant just supports my argument even more: Once you find a way to consistently kill enemies you are never required to change your strategy. You enter the encounter, perform your inputs with no regard to what the enemy is doing and you win, if your build is powerful enough. When what´s in front of you stops being relevant you´ll sooner or later realize that you´re repeating the same stuff over and over again.
