The trial is about if Google used illegal practices to suppress and harm competitors.
So the person testifying, literally, is the victim of the crime.
Hence why the opposing side gets the opportunity to cross-examine the witness, and why it would be a really bad idea to put forward a witness who clearly has a grudge against the accused. In cross you just show they have a grudge and now their testimony is suspect.
> Now, if they had actual evidence it'd be different
It is actual evidence. I don't think you know what evidence is...
Hard/soft evidence are established legal terms.
Even with a CCTV recording, you can use testimony to cast the CCTV recording in a light favorable to either the prosecution or defense. The circumstances surrounding evidence are weighed in order to come to a verdict or judgement.
Court cases are not about "who has the most incontrovertible proof", they are about convincing a judge or jury of an idea in order to get a specific outcome. Do not underestimate testimony (or really, any evidence that you think is inferior)