Why don't you have to establish why a deliberately non-balanced system is needed? Why is balance not good? How is it not open for debate?
This sounds a lot like OneTrueWayism more than anything else, but I offer you the opportunity to convince me otherwise.
I don't think so.
Games that heavily favor balance -- or, more precisely, heavily limit imbalance -- are universally games of competition. In those types of games, the rules exist to establish a fair contest. Sometimes they go so far to be a pure competition of only player skill that the only imbalance is who goes first (Chess, Go). They're also often zero-sum, adversarial games: you win at the cost of others losing. Even in games where co-operation is favored and balance is considered a requirement -- MMO raiding springs to mind, obviously MMO PvP is adversarial -- you're competing with other players for the same role. It's a market competition for a position in a raid rather than a direct competition.
With D&D, however, there's not really any competition inherent to the game. Now, you can certainly
add competition and make it a contest of who is most effective in combat, but that's never the stated objective of the game. That's one you've added. I mean, what is the objective of D&D? Remember when you'd play traditional board games, and the first thing they list is something like "Objective: Eliminate all other players" or "Objective: Reach the end of the board before all other players." What would D&D say? "To have fun with friends while you roll dice and tell a story about an adventure"? Why does game balance
necessarily lead to a better game result? Objectively? At all tables for all players?
What about the DM? Well, there's no contest with the DM. He can throw the Monster Manual at you at level 1. His role is to challenge, not to compete, and the DM can modify encounters as needed to adjust difficulty. This is why the DM vs Player mentality from late 1e and early 2e was so harmful.
What about losing in D&D? The only way you objectively lose D&D is when the game ends. You don't lose when you die. At worst, you get a new character. You never actually get eliminated from the game. Sure, you lose when you're not having fun, but since "fun" is subjective that doesn't make anything an objective requirement for the whole player base.
Look at something like, say, rogue-like video games like The Binding of Issac or FTL, where combat effectiveness ostensibly
is the goal. Nobody is going to argue that ??? has a better start than Issac, or that the d6 isn't a ridiculous starting item, or that few ships have a better start than the Crystal B or a worse start than the Engi B. Yet people still play the other characters and ships. Or, indeed, look at any game with a difficulty setting. Obviously, you're most effective playing on Easy. So, why do people play on Hard? Sure, some people might not be able to win on anything other than Easy, but if so, why not
only use Easy? I mean, these games could be like Spelunky, where every character is identical and there's only one difficulty setting (IIRC).
So, if the game isn't competitive, and the objective isn't to maximize combat effectiveness because even death isn't losing, and even if the objective
were to maximize combat effectiveness there are people who don't necessarily want to do that... why is balance considered such a Holy Grail of D&D game design? It seems to me like giving people dials is equally important. Even if
you personally want a highly balanced game, D&D is generally
not designed for a single play style. Allowing people to choose less effective options is a requirement, then. As long as conveyance is handled correctly and accurately -- that is, things that look powerful are powerful, and things that are powerful look powerful -- then there is no problem.
So, no, I don't see a case for tight balance in D&D. I think we got very close with 4e, and I think that game suffered quite a bit because of it.