There is no reason why you cannot ride 3-wide in one lane. How do you manage when people rotate off the front? At times, it would be 4 wide. Maybe you need to ride a tighter double pace line?
And yes, for those who are not strong climbers, going to the front, and maybe even off the front, at the base of a climb then riding at your own, slower pace as the group rides up at a faster pace, then attaching on to the back at the top of the climb is a recognized strategy that is employed by many.