I think this description does Sayers a disservice.
Her characters are more substantial than two people who can exchange ponderances on the news-of-the-world and-or literary analysis. As A.I. has proved, anybody can do those things (or, at least, look like they are doing those things).
Peter does appreciate Harriet's writerly occupation. And her intelligence is a given.
What attracts him to Harriet, however, is her fearlessness.
He attends Harriet's trial. In that trial, Harriet tells the absolute truth, even though it works against her and she clearly understands that it works against her.
Harriet is suspected of murdering her pompous, condescending lover who died from arsenic poisoning. Harriet ended the relationship because he offered to marry her. She had agreed to live with him based on his avant-garde beliefs, including the belief that "marriage is just a piece of paper." In the early 1900s, this decision made her a social pariah in some circles. His sudden offer of marriage made her feel like she is being offered a "bad conduct prize," as if all along she was being tested to see if she was worthy of marriage (based on the lover's character, testing Harriet was exactly what he was doing). For her, the principle of a thing isn't an abstract notion but a reality of day-to-day life.
She is, in sum, a kind of Nero Wolfe. An almost ruthless brain is at work behind her social poise. And Wimsey--who knows plenty of intellectual women and plenty of female artists (he has slept with a number)--is bowled over. Utterly smitten.
In Busman's Honeymoon, Peter and Harriet have an exchange where Peter admits, "I can enjoy practically everything that comes along--while it's happening. Only I have to keep doing things, because, if I once stop, it all seems a lot of rot...Now, I don't know." He was always running to keep ahead of his fears and possible depression.
Harriet, however, has always been more grounded: "I've always felt absolutely certain [that life] was good. I've hated almost everything that ever happened to me, but I knew all the time it was just things that were wrong, not everything. Even when I felt most awful, [I thought] of somehow getting out of the mess and starting again...Things have come straight."
That non-saccharine optimism is a quality that pulls Peter fiercely to Harriet. He would possibly get bored (as would she) if they weren't intellectual equals. But IQ is not the quality that makes the relationship. The ways Harriet and Peter separately tackle the universe are far more impactful.
Love is not something that can be plotted on a chart.
