I don't get what he is trying to do here.
He is accused of blackmailing party members, slacking, and leeching.
So to disprove this he has added the guild master (probably strongest person in guild) as substitute to the party and intends to take on a strong boss monster.
Even if he succeeds, won't the common folk think he just somehow enthralled the guild master too and is doing the same thing? The achievement will just be assumed to be because of the guild master's contribution. Unless he comes out on the god's eye thing, in plain view, no one will believe he contributed anything (like all the other healers do).
And I don't understand why the guild hasn't come out and said "Due to a recent article's accusations against an adventurers relation with guild staff, the guild's internal affairs has conducted an investigation into this event. After a thorough investigation, G.I.A. has concluded the allegations to have no credible basis."
With this, at least the common ppl won't auto assume gilt and immediately try to stone him in the street. Those in disbelief would at least ask Amy in person for verification.
Now that I think about it Amy's testimony in the street would immediately disperse this allegation. It's quite convenient for the plot that she is currently sitting in jail.