And I'm sure that the instructor who said that did not mean to imply helping the team is the only criterion for the value of learning something new. You're twisting it around. "Something new" is a tool or bit of knowledge, and I suppose it very well could be handling a camera/strobe, or marine science knowledge. Diving with at least one other person is the relevant context we're talking about here, not solo. It absolutely can't hurt, in learning something new, to consider how it might be employed to make your buddy's dive safer, more productive, more enjoyable or whatever, depending on what the goal of the dive is. Helping your buddy is certainly not the only reason to learn something new, but the instructor's suggestion to their IDC students to consider that reason in addition to the obvious ones really stuck with me.This is nice, but is not the only criterion for the value of learning something new. Does learning how to control the power of my strobe to match the ambient light help the team? Does knowing that is a French Grunt and not a Bluestriped Grunt help the team? Does realizing that most of the life I see underwater is animal and not plant help the team? Does the skill set and equipment configuration to safely dive Solo help the team? The team is just one way to dive, and GUE teaches it pretty well. But it is not the only way or reason to dive.
The anecdote about what I overheard an instructor say was just a footnote to the main point of my post, which is that aiming for a high level of precision is not "egocentric." Being able to achieve a stable position and more precisely control one's position in the water without having to devote too much brain bandwidth and/or physical exertion to it enables a diver to better focus on whatever the task is at hand, whether that is sharing air, deploying a DSMB at a safety stop, or just taking photographs. Your point that "perfect" trim is not required for this is well taken, but as I said, aiming for this higher level of precision in a course or on practice dives is what may make the difference when something actually goes wrong and you revert to whatever level of precision you can muster.