I think you'll have a hard time arguing that last point. The games that tend to stick around are typically examples of the best-balanced mechanics out there.
Actually, the reverse is true.
It's hard to think of a long-lasting highly balanced RPG, save for the "toolkit" systems like GURPS and Hero. They are balanced within themselves because they contain a system of rules for creating RPGs rather than characters. The play group can put a lot of thought into what they want to play and build a sub-set of the game to emulate that thing.
Traveller balanced? Buh-ha-ha. The 19 year-old skillless Merchant washout and the 39 year-old highly decorated Admiral with a dozen skills would like to have a word about "balance".
Oringinal D&Ds (0e, 1e, Holmes Basic, Moldavay Basic) weren't balanced in the same way, with the whole Magic-User / Cleric / Fighting Man using different systems.
Call of Cthulu? Starting characters
can start reasonably balanced, but it uses random attributes, the dreaded "combat and non-combat capabilities draw from the same set of resources" that people decry as a balance-killer and once the Mythos books appear balance flies out the nearest straight angle.
Villains and Vigilantes? Aftermath? Tunnels and Trolls? Chivalry and Sorcery? Runequest? Gamma World? Rolemaster?
What long-term games are you thinking about that contain heavy balance?