You're absolutey right, LoLevel.
I just would like to add a few things:
There's lots of limiting factors, tfc amount being just one of them:
Noise abatement procedures (for mainly political reasons)
Lack of civil airspace (meaning too much airspace being used by air force)
Unnessecary requests increasing complexity and limiting capacity (prime example: Lufthansa pilots asking for level change due "light turbulence"!)
Unnecessary messages like:"approaching FL..., maintaining FL..." (thank you very much, but we are radar equipped)
I can only speak for Europe, but it wouldn't be much different in Canada or USA:
The tfc amount is more and more sheer madness, despite of slot allocation.
AIRLIFT, get yourself an idea about the coherences and visit an ATC unit.
It will open your eyes!