Not so at all. I've played a lot of games at 28 (weighted) points and have seen 28 point monks and paladins pull their own weight in combat.
Str 15, dex 10, Con 14, Int 10, Wis 12, Cha 14 is a perfectly playable set of stats for a paladin. Such a paladin can easily pull his own weight in a campaign if typical fighter stats are
Str 16, dex 12, Con 14, Int 10, Wis 12, Cha 10.
Similarly, a half orc monk with
Str 18, Dex 12, Con 14, Int 8, Wis 14, Cha 6
is an excellent bruiser in the 28 point campaign.
A regular monk with
Str 16, Dex 14, Con 12, Int 8, Wis 16, Cha 8
also works quite well.
28 point buy sorcerors work well too
Str 10, Dex 14, Con 14, Int 12, Wis 10, Cha 15 works well. (That was my initial setup for a 14th level sorceror I played in a high level campaign).
A sorceror who wants higher DCs could go:
Str 10, Dex 14, Con 14, Int 10, Wis 10, Cha 16
I've seen a highly successful 28 point sorceror with
Str 8, Dex 12, Con 12, Int 10, Wis 10, Cha 18
The thing about 28 point buy is that you have to accept that your character will probably have some weaknesses.
Ridley's Cohort said:
I think that you need at least 32 points to make a monk or paladin that can carry their weight during combat. Even those characters will be a bit marginal.
At 36 points I have noticed that monks & paladins can fill out some of those "secondary" stats to 14 and they look competitive.
Don't have enough experience with bards or sorcerors to really comment.
A 28 point buy campaign works very well if you stick to fighters, barbarians, rangers, rogues, clerics, druids, and wizards.