You (Nellisir) have tried to head-off concerns about mechanical effectiveness as a distinct and important category of effectiveness by you remarks about the GM being able to beat any PC, and challenging all the players and giving all the PCs spotlight time. But those strategies only work (I think) in a game which is very heavily GM driven and correspondingly passive on the player side.
I'm not sure that I agree - or perhaps I do, but that style of disinvolved DMing is more CRPG than I practice. I do tweak encounters on the fly to make them more interesting; I don't just play them right out of the book. I don't believe that requires passive players.
The DM sets the entire world for the players. Sight, sound, smell, sensation, encounters, challenges, difficulties. If a rogue wants to become a paladin, that suggests that at some point, an order of paladins was introduced and given some detail -- probably by the DM. That doesn't mean that the players can't dictate their actions within the world - they can and should. They choose where to go, what to do, what quests to take up or drop, etc.
I see my job as taking the players' choices and making them interesting and meaningful. Every player should have fun. If you're not having fun, then we need to talk and figure out what the problem is. Maybe your character hasn't had much to do recently. You could take a level of fighter, or I could put a few more traps into the game. The first implicitly validates the view that you made bad choices. The second acknowledges my role in making your choices meaningful.
In a more player driven game, a player who wants his/her PC to be effective in genre terms also needs to have adequate mechanical effectiveness.
The more you remove DM judgement and oversight from the game, the more mechanical effectiveness matters in validating a player's choice. That makes sense.
I'll be honest; I'm used to homebrew adventures and house ruling things. I don't do pre-written adventures; at least, not without a lot of customization. As I said at the beginning, I don't believe that requires player passivity. My job isn't to tell
my story, it's to make sure everyone has fun (and your job is to also make sure everyone has fun) and if we're lucky, we all have a story. Without a fixed script for the adventure, it's impossible for anyone to get off track or miss the adventure - if that adventure doesn't suit, we'll try a different one.
(And as far as beating PC's...it's not something I advocate. But there are players that see the game as an adversarial relationship, where their job is to "beat" the DM, and that doesn't work for me.)
Edit: I write this, and then I see this on the WotC site..."
Its goal is to present combat as a challenging puzzle that pits the players against the DM, capturing the best parts of 4th Edition." http://www.wizards.com/dnd/Article.aspx?x=dnd/4ll/20130923
Edit edit: This sounds cool, though: "
An optional system that cranks up character customization by allowing players to build their own subclasses. This system is really more of a set of guidelines that let you mix and match abilities pulled from subclasses within a class. You can approach it as a DM tool (“In my setting, the wizards of the Burning Isle combine illusion and necromancy”) or as a way for players to have more choice in building characters. We’re making this system optional because we know that some players want a lot of ways to customize their characters, but more customization invariably leads to broken combos. We can manage combinations and fairness at the subclass and feat level, but slicing things much finer than that goes beyond what we can reasonably expect to playtest."