We don't need Witnesses to relay their opinion

Really? Witnesses testify to what they witnessed/heard first hand. What the White House released was a summary of the call, not a verbatim transcript. One of the major complaints about the whistleblower was that they were relaying second hand information. Lt Col Vidman was on the call and had raised concerns early on.

Anyone who takes issue with or tries to diminish the need for his testimony is simply afraid of the truth.