In principle, I agree.
In practice, I see a fair amount of players who have very different approaches that often convey very unequal notions of common sense. For example, it does not follow to me that if said swashbuckler puts his highest ability score in Charisma and skimps on the physical scores, he should be able to do daring stunts because charisma makes you cool. But some people might disagree. To me, such a character is and should be somewhat suboptimal.
None of which means that a player shouldn't play such a character.
Here is the thing, lets take the (IMO) way you say shouldn't work. I don't see them ditching all physicals, but lets say they go 10 Str, 14 Dex, 13 Con 15 Int, 14 Wis 18 Cha... and they say "Well I'm a swashbuckler that always gets the girl, I'm also really smart, able to fight things smarter not harder"
He is a 1st level rogue, he is human so he gets 2 feats and says "Weapon finesse is awesome... I'll take that, and weapon prof in the rapier..." then he puts skill ranks in bluff and diplomacy and jump and tumble and cross class in know arct and engineer. He has +2 to hit for 1d6 damage with an 18+/x2 crit. he can with combat advantage deal +1d6 He has 7hp His AC is 13 or 14
The druid of the game takes a wolf... it has 13hp, +3 to hit 1d6+1 damage and trip, and an AC 14
that isn't the druid... it is one class feature...
Again, I agree in principle. However, I find those are corner cases. Most animal companions are modestly effective compared to martial characters, even with full buffs, and clerics tend not to spend the resources to be effective fighters.
I've never been on record as defending, say Divine Power as an appropriate spell. I'd revise it. However, I think in general the 3e cleric as a whole is about right balance-wise.
OK, lets go to a 5th level fighter...
He gets a +1 to a stat and it will be str, but he starts with 15 str 15 dex 14 con 11 Int 12 wis 10 cha
he isn't human, so he has 5 feats, we will take weapon focus and specialization longsword, Dodge, mobility, power attack
+9 to hit 1d8+5 damage 19+x2 crit. He has a 19-20AC and 40hp
he can power attack up to +4 1d8+10 average damage no PA is 9-10 w/full PA 14-15
the 4th level druid has a bear...claw/claw/bite +6/+6/+1 1d4+2/1d4+2/1d6+1 with 13 AC and 19hp (next level is +1 str +2hd and +2 AC)
BUT... if the druid puts any buff up he shares it... so lets cast 1 spell... Bull str and remember he himself can be a bear helping... but we are just talking the companion here
+8/+8/+3 1d4+4/1d4+4/1d6+2 Average damage not buffed 13-14 or w/buff 18-19...
the fighter has to full power attack to get average damage up to the bear... and can't hit the buffed amount on a bet.
tell me why 1 class feature of the druid is 3/4 as good as a combat focus fighter?