There's no denying that full casters/manifesters of any sort are broken in 3.5 once you approach level 10 or so, but they're overpowered even before then if you do it right. You point out Suggestion at level 5 for a save-or-lose vs. the Fighter, consider Color Spray at Level 1 - also a save-or-lose vs. the Fighter, and relative to its level, a more powerful one...it's an AoE spell that can hit multiple people, and can actually cause that fighter to die; unconscious creatures are vulnerable to a Coup De Grace insta-kill, where the worst you can do to someone under a Suggestion is make them stop hitting you, or do something nice. Furthermore, balance is only really relevant in between party members - it's not that a Wizard can cast Suggestion and knock out the Fighter, it's that he can cast Fly and Wind Wall and be invincible to any monster who can't also fly, or cast Fireball and kill entire swarms of enemies in a single hit, or cast Solid Fog and effectively paralyze a group of enemies (or cast Solid Fog, then enjoy several consecutive turns of Fireballs against an enemy who can't counterattack him without magic of their own). All a fighter can do is hit things. As an entire party of wizards, we're all equally powerful (or overpowerful, depending on perspective), and thus the DM can simply ramp up the difficulty of fights.
All that ranting aside, Liking low-levels for their power differential is valid (incidentally, that's why I love the E6 variant - 6th level is probably the single most balanced level in the game in terms of class differentials, and gives everyone a distinctive 'trick' that defines them), but that has nothing to do with the roleplaying, which was your initial claim. Any archtype or character you could play at 1st level, you could play at 5th level or higher, unless "dies to a single dagger stab" is considered an archtype.