You are both taking what I said to some extreme. Yes, it's not necessary for every character to equally contribute all of the time, which was never what I was suggesting.
It is a good thing when one avoids scenes where characters have nothing to do. Sometimes, it will happen (it's not so good to have too many party spokespeople, for instance), sometimes the player would rather grab a bite to eat, or whatever than participate in a scene. But, the problem I see far too often is one of irrelevancy. D&D has always been designed with the intent that combat was a group effort and the primary means of overcoming obstacles, so it and its knockoffs fairly well avoid the problem.
The comment I responded to, mainly because I love ranting about how awful the soldier is in this game, was taking a black and white approach to the issue. Somehow, a middle ground of characters being constantly engaged while retaining differing strengths keeps getting lost.
Rather than establishing scenes where some of the party serve no purpose, I believe it behooves a GM to try to create scenes and situations where the entirety of the party is engaged. Now, I think this is a lot easier by splitting parties up, easier for the players anyway, much less so for the GM. To avoid the problems that causes, I actually wonder how many articles have been written on how to create scenes that keep everyone involved.