Yes, you need 3's. Defenses want you to take long 2's. It is also easy to rotate to guys inside the 3pt line and it is easy for defenders to collapse the lane if they don't have to respect their man standing on the 3pt line.
What does spacing mean? It means getting defenders away from your teammates so the defense can't help without risking you getting an open shot.
The lack of big man in the paint is not due to a lack of skill. It is due the lane being packed due to the modern rules and defensive strategies.
Due to the focus of defenses on clogging the lane and running guys off the 3pt line, there are a lot of opportunities for guys who can bury the inefficient midrange shot efficiently since that is what teams give up. But since 33% from 3 is as efficient as 50% from 2, you have to be darn good from 2 before you can really space the floor from 2.