I don't think Guthrie was unfair, but Trump more than held his own throughout.
Guthrie acted the way she did to mollify NBC employees who resented NBC giving Trump debate time at the same time as Biden. They did not want the Trump event to detract from Biden's attempt. That ought to tell people something about the depth of the bias of the media.
Trump held his own against a moderator with both a political and a personal agenda. He's had to debate the moderator in his first two (2) events. Joe Biden hasn't had to because the tough questions (Hunter's corruption and how Joe is part of that, giving Antifa and BLM free passes on violence, court packing, our policy on China, and specifics of Biden's COVID-19 plans that are actually different from Trump's, and disclosure as to his own health information) were not asked by Biden's moderator on the other network. The "undecided" voters on Biden's "town hall" included a former speechwriter for the Obama White House. (That man should be confronted by reporters and asked why, as a member of the inner Obama White House is he "undecided".)
Why can't Joe Biden be in a nationally televised event vigorously questioned by a Republican journalist who's not a #NeverTrumper? Why can't he be asked about why he won't condemn BLM and Antifa for their violence? Why can't he be asked about Hunter Biden and the corruption that is beginning to may Biden look like Spiro Agnew? Why can't he answer questions about his role in the Presidential transition during which he suggested application of the Logan Act against Michael Flynn; about what he knew and what Barack Obama knew about these events?
The answer is that Biden CAN, but he WON'T. He won't because he's a fading coward who now (apparently) has something to hide that will contaminate his Administration from Day One. And now he's all about the money. The Big Tech Companies won't be able to hide this, and it's going to be awful if (and, IMO, when) the Hunter Biden issues cause people to see Biden as Agnew, "the big guy", "my guy" taking payments. Taking kickbacks from his own son is how the e-mails read.
An interrogation for Trump. A friendly interview for Biden. That's what happens. Is that honest? Is that putting first the interests of honestly undecided Americans who are seeking honest answers to serious questions? Biden is getting a free pass, and now the free pass is on Spiro Agnew-esque behavior while VP that is coming back to haunt him, but that Agnew-esque legacy of Biden will also haunt all of America if he's elected.