I have not read The Science of Happily Ever After in over 6 years now, but I don't remember there being a formula - what I remember is that you really only get 3 non-negotiables before you narrow your dating pool so much, so you need to make sure your non-negotiables are something that will lead to a partner with whom you are likely compatible.
After reading this book (as well as an article in The Atlantic called "Masters of Love" - also from 2014), I thought about it a lot and my 3 were; kindness, supports himself, actions match words.
Then I had the best single summer of my life and met my now-SO (of 5.5 years) when I was least expecting it. I likely would have broken up with him after a few months for a ridiculous reason, but I thought about the book and realized that with all of his good qualities, breaking up because of something completely silly was not a smart move since the relationship was progressing well in all aspects that actually mattered, and he had my big 3. And I'm so glad I did.
Where I think this book helps is people who are choosing superficial non-negotiables. I have a friend whose non-negotiable was: has a man-bun. So she dated a ton of guys who were completely incompatible with her because hair has nothing to do with compatibility! (She is in IC, read the book, and is now happily dating a bald guy for over a year.)
My SO has a friend and I've explained the concept in the book to him because he's been single for over 6 years and really wants to be in a relationship. His 3 non-negotiables? She must be at least 5'8", constantly wear high heels, and be a beautiful blonde. He actually joked that there are probably only 6 women in the country that meet his lofty requirements. None of those things matter about who will be a good partner! (And guess who still hasn't been on a date in over 6 years?)
I also remember reading something about being careful about chemistry or just knowing as that often means the person has very similar qualities to a previous relationship, and you feel that chemistry because it seems familiar. One guy I totally fell for and dated off and on for a few months, with hindsight, was so much like my WXH. So glad I dodged that bullet!
All this to say, I think it depends on how you define settle. I loved being single, and was not willing to settle on anything important to me, but if I were designing my ideal partner, he'd have other traits than ones my SO has, so in a way you can say I settled (and he would say he settled because of certain interests I do or do not have).
Like I'd love to have a life partner that ran marathons with me (I actually had that with WXH, and it was fabulous!) But I'd rather have a quality person who is supportive of my running, plans trips so I can run a marathon in a new state, and drops me off at 4am to catch the bus to the start line.
To answer your last question, I do think OLD plays a role in this. There's no getting to know someone in person slowly, like through an activity group, which makes the first date pressure-filled for many. And if the person doesn't come off 100%, you know that there are dozens or hundreds more that you can date (depending on your location). When I was first OLD (and not ready to date), I had so many ridiculous reasons for not having a second date with someone - part of this was me not being ready, but I also knew that it didn't really matter since there were many more where that one came from. Not proud of thinking that way, but I had many guys tell me the same thing.