Why is this even a question. All you have to do is listen to his speech! Whether someone else wrote it or not is moot, he spoke the words that directly incited the insurrection.
I agree that it shouldn't even be a question, but I know someone who has a high IQ who actually couldn't believe Trump incited the insurrection. Now we have concrete evidence so people with this POV have no leg to stand on.
If I invited a heap of outlaw bikers to Mar-a-lago, and they started trashing the place. Then, ultimately, I would be responsible for the damage they caused because I organised the event. So, yes. Trump IS responsible for what happened because he invited them to his rally and directed them towards the Capitol.