There is no magic formula to settling down. Bea was following the same "get to know you" formula with Dave Clark and he dropped her after 10 years and married someone else a relatively short time later. William did confess publicly he was too young to marry and he also was seeing other women. So I don't think it exactly was a "thought out" formula. I think Kate would not have said no if he proposed as early as 2007.
Charles himself confessed he was interested in someone else and preferred her to Diana (he confessed this to Dimbleby). William was not in the same situation by any means.
Harry dated Meghan for about 2 years so it's not like they impulsively boarded a plane and married in a chapel in Las Vegas.
He wasn't seeing other women. Before Kate yes but after Kate no. Just like Kate herself had boyfriends before William. Why would you say something like that...... That's just wrong. And how would you know she would have said yes if he proposed to her in 2007.... Maybe they both didn't want to marry at that time. They both said in their engagement interview that they began talking about marriage about a year before they get engaged...Stop projecting your ideas about people you don't know and stop reading tabloids.....