For a game I would have to say more than likely because it
a) makes for more diverse options and no 'best' way to do things
b) its not much fun being overshadowed by another player
c) all players like to fulfill some position in the group, even though it may not be what everyone considers the most glamerous
Though alot of factors come into play when determing whats balanced.
As an example (I dont realy want to retruge the champion issue again):
For me I'm one of the few people that dont think the 2nd ed Champion career is over-powered, simply because a player still has to pay for everything they get out of the career, while others think it is because it has a breath of high characteristic numbers that can be achieved.
My view is that by a third tier (an advanced career only accessable from an advanced career) career the bounds are off and a player needs to spend alot of XP on getting a character up to reach those lofty characteristic potentials, while a character going another path will spend them on something with less potentially stat hights but other benefits such as allies. While for others the factor of having to reach those heights is less significant than the heights themselves.
Conversly for me the Targeteer is much more overpowered career since its a secondary career (an advanced career accessable from a basic career) that can reach extreemly high points (just shy of the maximum possible in the game) for alot less cost. While others dont have an issue with its high characteristics because its in but one characteristic(balistic skill).
For me balance in 2nd edition is covered by not only the tiers but the number of advances to reach the career's completion and potentials, the suitable exists the career has, what non-characteristic advantages a career requires or gives and any weaknesses that may be inherant (or developed) in going along the path to the career itself.
Ultimatly balance means different things to different players/GMs but humans have the notion of whats 'fair'. Sure its often different between people, but its generally their in one form or another.