truth in this. From what we were taught, it is a known fact that 1950-1980s Singapore CHIchess veterans rely more on their mid-games rather than their openings. Opening info/theory were at its infancy then.
This is the same reason why we were trained in our first opening only at a very late stage by our mentors. Even with our training, our mid-games are still at baby steps because of its complexity and we are constantly learning.
Our mentor says: The best opening is the one that exposes the enemy's weaknesses, not the situational perfect moves or what other people think are the better moves.