I don't disagree that he could have handled it better. Hell, he's a horrible debater. I'm sure in part because he's not a career politician and in part because he's arrogant and not used to being questioned. But the idea that he could have said anything that would "shut everyone up" is absurd and we both know it. CNN was caught on tape admitting that they made up stories about Trump and portrayed Biden in a positive light every time they could.
When asked to denounce he said sure I will and then immediately jumped to Antifa. As you mentioned that is horrible for a debate and for the sound bites that all of the MSM will of course use but that's not the same as not answering the question at all or saying "no, I will not denounce them". He put them on the same field as Antifa and we know how he feels about them.
You pick and choose items that fit your narrative but don't fit all of the facts. Indignation seems like a pretty natural response for someone who is not a career politician. Also, he told the Proud Boys to "stand down and stand by". Some people might give him the benefit of the doubt that the second part was a slip of the tongue but either way he clearly said to stand down. For some reason you just pick the part that makes him look the worst. Not sure if that's because that's what you heard and just didn't bother to look into it or you are willfully omitting facts.
Also it's pretty unlikely that the Proud Boys are even white supremacists as they were led by a Latino. But again for some reason these facts get omitted. I'll assume you don't have ill intent and are just misinformed.