Really? Friends can help you do mock interviews for asylum? LOL. This is exactly the kind of advice that will end up getting you referred to court.
"Lawyers can't help you prepare cases" = Wrong. My attorney prepared my entire case from beginning to end.
"Lawyers can't help you gather evidence" = Wrong. My attorney gathered tons of relevant evidence of country's conditions specific to my case from dozens of reputable sources, some I had never even heard of.
They're not coaching you into making up a story. They help you tell your story in a way that's consistent with immigration laws and relevant to your particular case. When I applied, my attorney handed me an I-589 (application for asylum) and asked me to fill it out. Once I did, he sent it back to me asking tons of follow up questions asking for very specific details while helping me reword certain things in a way that made sense. We did this 4 times total before submitting it. He helped me put random events, people, and places into an actual compelling story. The entire story was mine, nothing was coached or lies, but the level of applicable specifics and details that went into it were definitely key on winning my case. These were all things I would not have thought of had I done this on my own.