This can be avoided. I’ve been the walker in the group of three riding. You just need to pay attention, be ready to move when everyone has hit, and find creative ways to get to your ball. If I’m closest to the green, I’ll frequently walk outside the rough in the trees to get even with my ball. When everyone after me has hit, I’m generally no more than 30 seconds to my ball.
Same thing on the green. If you’re not the last guy in the hole, it’s a good idea to violate normal etiquette and start walking towards the next tee. If I’m on a course with a long walk between a green and the following tee, I’ve hooked a ride to the tee with the guy riding solo.
I’ve played rounds in 3:15 doing this. Walking alone, I comfortably play 18 in 2:25. Many years ago at Pinehurst, I played about 12 holes on No. 5 in a cart in about 40 minutes–but I was flying because it was a short day in February and I wanted to get in some more golf before dark. I specifically chose to go out on No. 5 because I knew there weren’t many golfers on the course and many of them had teed off hours earlier.
The Scots regularly play in groups of four walking, and a three-hour round is the norm over there. I can’t imagine anyone saying that they enjoy a round of golf where they have to wait on a lot of tees and fairways for the group in front to clear. I’ve found that you can start running into that phenomenon when the rounds stretch out to 4:30 or longer.