He didnt bring an army of heroes with him. You act like he led or had any control over the Avengers as if Captain America wasnt bringing them regardless. They stood back and Thor and Hulk were not hitting him in the face in that moment. When Xavier went up against Scott, none of those heroes were attacking Scott save a single arrow which came from Hawkeye. It was just Xavier and Scott at that moment. It was a sound strategy.
When Xavier fought Dark Phoenix, he had the rest of the X-men by him and they attacked Jean alot more than what we saw the Avengers do in AvX 11 when Xavier confronted Scott. Scott wasnt strong enough to fight the rage and gave in and killed Xavier. Jean was despite having Storm, Collossus, Nightcrawler, Wolverine and Beast all physically assault her and Xavier using his full power to restrain her. Thats why I dont think its accurate for you to say his past experience should have told him that what he was doing would be a failure when thats quite the opposite of what actually happened