so this thing...
One of my players reads this blog, and he was explaining this post to me the other day. There are some things to like about it: "Treat The Environment As Another Enemy" is a great way to make things interesting and might be rule #2 of good encounter design.
But "Make Sure Each Player Will Have Something To Do and Give Each Player A Unique Role"? Come on. The only example given is for D&D, so since we're not playing GURPS (where we spend several hours doing math so that each character is different), we'll talk about that. Cross-posted from my comment:
"There’s a reason the classic D&D party is a Fighter, a Mage, a Cleric, and a Thief."
Try playing Original D&D with only one fighter. I dare you. See what happens.
This kind of thing is a direct result of the edition power creep that we've had over the last 25 years. In 3.x D&D we have 2000+ feats to choose from for "infinite customization," but every fighter just chooses Power Attack because it's the best. If you have two fighters in your D&D party, of course one will be better than another, because they'll both prioritize Strength, then CON or DEX, etc. And they won't roll exactly the same stats. One will likely have a higher strength and since so much emphasis is placed on stat bonuses to create a "viable" character, the guy who rolled low is left in the dust. This is the "my precious character" sort of thinking which characterizes the current state of the hobby.
This is, by the way, in direct opposition to your other stipulations: to not say "this monster's invulnerable to swords!," "avoid the roll-fest" and "treat the environment as another enemy." In these contexts, whether your fighter has a +1 to damage rolls or a +6 won't affect the solution you, as a creative player, come up with.
And if you *can't* come up with anything to deal with a monster that's invulnerable to all your plusses, well... I don't know how to help you.