The so-called extensive research that parents are doing really has no bearing on what type of couple the children will be together. Knowing that a bochur is a good learner, says nothing whatsoever about what kind of husband he will be (other than probably continue to be a good learner). Knowing what seminary she went to says nothing about her chessed, compassion, cooking skills, love of children, affectionate nature, etc. The research usually involves the asking of questions about naarishkeit (type of tablecloth, plastic vs. china, tied shoes or loafers, etc.).
Until two people spend both qualituy and quantity time together, you can ask all the questions you want and everything can look perfect on paper, but the shidduch is still NOT GOOD. A couple needs to spend time having meaningful conversation about their hopes and dreams, the path they want to follow in the future,the kind of family they want to raise. It is less crucial for them to spend that same time discussing the very superficial things that these couples often discuss, because they have (naturally) not as yet reached a sufficient comfort level with each other to make deep conversation.
People who rarely see each other during the engagement period (in order to avoid stress and sniping at each other), are probably also people who have not yet learned how to constructively disagree with someone and still realize they love that person. If they cannot disagree “safely” before marriage, what makes you think it will be better AFTER marriage?
IMO (and I acknowledge I could be wrong), people who date for short cycles (3 or 4 dates) and get engaged, have an intrinsically lowered expectation regarding dating and marriage. And if that works for them, who am I to say it’s bad for them? But when one has lowered expectations and then gets disappointed (because even with lower expectations, there has to be a minimum of something good going on in the marriage), that disappointment is demoralizing and disillusioning, and that’s why there is a rising divorce rate amongst certain groups that normally had a much lower incidence of it.