That is a timeless question and one that is very hard to answer.
Once you have more than one person you then have CRM to worry about. Some brighter minds work better on their own and can find it hard to communicate their thought processes.
Also, modern jets can look after the flying side to the extent that the single mind can easily manage the systems.
Many years ago, before cockpit ergonomics were really considered, I would agree with you. Nowadays though I think the single person crew concept in a fast jet is far more preferable.
I am not the leading expert though and others may well disagree.
BV