Milk do you think Fuller chose an actress who wasn't attractive on purpose as Molly? Not to shit on Nina, she's objectively not conventionally attractive, but she's also not Will's type (considering Alana whom he was actively trying to get with and according to Dancy was very interested in).
I am pretty sure he chose her because of the dynamic she had with Hugh Dancy on Venus in Furs. But regarding Will and Molly, yes, I think the intention was to show there was no heat/passion there, taking into account that they deleted all of the more intimate interactions between them from the final cut.
Will would never choose, at that point, anything that ignited a flame in him. Molly was mourning and so was Will, that’s why they bonded. That and I suppose lifestyle similarities.