I think this is the best advice of all. The efficient-leveling advice is good, but following it, one will eventually end up with a sort of "vanilla" god-like character.
The Oblivion leveling system, while frustrating at times, is actually working as intended. The idea is that different characters will have different strengths and weaknesses, and that the game will get harder as one goes along, presenting greater challenges to be overcome.
The game does actually give us everything we need to succeed. Pure warriors are able to start with high Endurance, and quickly increase it to massive levels. Stealthy characters build upon speed, luck, and sneakiness. Mages acquire nearly game-breaking Illusion spells as they arrive at Journeyman level. And everybody gains from Alchemy (the ultimate secret for virtually all builds.)
Yes - this is true, but I find it a bit limiting. The game does indeed provide everything a character needs to survive the tougher levels, even with a most-used-skills as majors build and no attention to leveling, but that "everything" pretty much consists of alchemy, illusion and enchantments. And the difficulty bar.
I rib Zak for playing Zakarius Svedlin the Imperial Atronach Alchemist over and over, but I understand why he does it. That's the build that functions best with the vanilla leveling system (not necessarily being an Imperial named Zakarius Svedlin - you know what I mean). But I want to play.... Lud gro-Dalum the freelance Orc adventurer, who travels the world mostly bare-chested, only grudgingly putting on a fur cuirass if he goes into the mountains, who has no interest at all in the Mages Guild or any of the schools thereof and who thus relies entirely on remarkable weapon skills. Or Mindi the Bosmer Barbarina, who floats through the world, not paying much attention to much of anything beyond whatever catches her eye at the moment and who rarely seeks out fights, but defends herself (and her friends) with jaw-dropping violence when necessary. Or.... so forth. Since I loathe efficient leveling and just want to play the game and lose myself in the character, pretty much the only way I can play those characters the way I want to play them is to very deliberately and precisely metagame the build. Because otherwise, they're going to end up Alchemists or I'm going to have to fiddle with the difficulty bar, and I'm just not all that interested in either one.
But yes - pretty much any character can be played within the confines of the vanilla leveling system with a judicious application of alchemy, enchantments, magic (and particularly illusion) and the difficulty bar.