It all seems inconsequential after recent events, but we have to carry on as normal or the bastards have won.
So, for fadec_primary_channel the answer is straightforward, cheating results in a medium term reduction in capacity.
If an ACC declares a capacity of 50 flights per hour and regularly receives 55, it won’t take them long to reduce capacity to 45.
The most common causes of overloads in ATC sectors are aircraft departing outside their slots, and flights turning up at other than filed levels.
Bear in mind as well that even with the existing slot tolerance of -5 +10 that a sector with a capacity of 60 flights per hour can in theory receive 75 flights; 10 from the previous hour and 5 from the next hour.
Increased flexibility would have to mean a reduction in capacity and therefore increased delays.
CIV5C: What you say is partly true, the controllers could keep you at your flight planned level, but that too is very inflexible. Many aircraft operators are perfectly happy to brief their crews according to flow requirements, I don’t see why you have a problem with it. The alternative, as Davey Clark suggests is to give you an “arrive position XXX at time YYYY and FLZZZ”.
That strikes me as being much more cumbersome. Correct me if I’m wrong...