I thought Cohen he said he had no knowledge that Trump or his campaign colluded with Russia.
I assume you didn't watch. He claimed he had no direct knowledge of collusion (undefined) but had his suspicions. But as I said, he confirmed he was working on the Moscow deal the whole time with Trump's knowledge and input, he confirmed that he heard Stone talk to Trump about the Wikileaks email dumps in advance, he confirmed he thought Jr was setting up the meeting with the Russians in New York. As long as you don't consider any of those things "collusion" because they aren't directly talking about "we are going to help you win the election", then yes. For you, those dots don't add up to anything. For other people they do. Remember that he was specifically told he wasn't allowed to talk about Russia details, so this is the stuff that was generic enough and already known enough that he was allowed to talk about it.
One of the things I liked about his testimony was he was fairly careful not to get out over his skis. He had all kinds of opportunities to say damaging things about Trump that would have dominated coverage for several days if not weeks, but didn't do it. That was a huge problem for the GOP strategy of "everything you say is a lie and you can't be trusted". If that's true, then by denying it, Cohen was actually saying Trump and Russia directly colluding quid pro quo was true, Trump beats his wife, Trump has a love child, etc. I understand why they went with that tactic (although refusing to defend Trump in any way didn't seem tactically sound) but I don't think it was as effective as they would have liked.
As for the dog and pony aspect of it, that is an issue with the open hearings. The closed hearings tend to be more serious - which is maybe why the Republican members mostly didn't bother to show up. Since they don't have a defense, they were only playing for cameras. Even the open hearing gave us what --- a half dozen to a dozen new Trump crimes to look into? A list of witnesses to call to verify those allegations Information that there are still ongoing investigations Cohen is helping with.
These things are an ongoing process. I am not sure why people think it will be a 1 hour meeting and boom, everything solved. This isn't a courtroom drama.