We get this thread every few years and we find out how fast a single and a two ball can play-which requires minimal cooperation between players.
Unfortunately, on a post pandemic full busy course, the pace of smaller groups isn't relevant, and such smaller groups can slow down larger groups by continually playing through(great if space allows but just doesn't work if there's nowhere to go and every single play through adds time to the slower/larger group).
the real key to busy course flow is teaching groups of 4 how to play ready golf, and maintain a consistent pace throughout the course.
So many just aren't ready when it's their turn, begin a long routine AFTER it's clearly their turn,take too many practice swings, start a long story when it's someone's turn to tee off(rather than when they are walking), don't read a putt when others are playing, don't grab a couple of clubs when parking a cart remotely or sharing a caddie--or worse yet refuse to proceed without a caddie's input-who may well be performing other duties.
In short it takes a coordinated effort for any group to play 4 balls at a sub 4 or even a 4 hour pace, and frankly all it takes is a couple of groups not doing this to slow the whole day down.
Competitive golf, well,as i said fast players either learn to play slow or just stop playing competitive events if there is not proactive pace of play management.The MET PGA does a good job with this, but in fairness most of our events are not played on modern pace of play monstrocities, and when they occasionally are-it grinds to a predictable halt.