Two and four stroke outboard motors are made to be run at high RPMs. They are more efficient in the upper end of the power band.
Why a dealer would tell someone to run only at WOT is beyond me, but, if your neighbor would like a second opinion, have him visit the Honda web site and submit a question directly to the technical support folks there.
Having such information as boat manufacturer and prop information will help them a bunch as well.
Honda has offered a four stroke outboard for a very long time. They are a fine engine and hold their value quite well. I'm sorry to hear he has had trouble with his.
Quit complaining about the color, just pull up your skirt and fish! -- snagged