Why would Elyot say that he and Amanda would have been perfectly happy with Victor and Sibyl?

Elyot says this because their new marriages, had they not run away, would have been calm and even, if not a little boring. Sibyl and Victor are good people, if not exactly suited for people such as Elyot and Amanda. However, Victor and Sibyl would have loved their new spouses as much as they were able.