I don’t think anyone expected Comey to produce any evidence associated with an ongoing investigation, for a couple of reasons.
First, the investigation into whether or not there was collusion between Russia and the Trump team is ongoing. The details of the investigation are classified until the investigation is complete.
Second, Comey was fired, and has no knowledge of the progress of this investigation since that point. Without knowing where the investigation has gone or how it’s progresses, it would be pointless for him to talk about it.
Comey was there to testify not about the Russia collusion issue, but about the details and content of his meetings with Trump. And he did.
As far as obstruction of justice goes, Trump could be guilty of that if A) Comey was telling the truth and Trump pressured him to drop the investigation of Flynn, and/or B) Trump fired Comey because he believed Comey and the FBI were getting too close with their Russia investigation. However, we need to wait for the completion of the investigation. If it turns out that Trump or any member of his campaign team colluded with Russia to influence the 2016 election, and if Trump had something to hide and fired Comey for that reason, Trump could be in some deep legal trouble. He’s already in a fair amount of trouble over pressuring Comey to drop the Flynn investigation, which is why Trump and his lawyers are doing their best to paint Comey as a liar.