To be honest, I don't have a CT dust extractor, but I do have a Porter Cable. The one thing I notice when I'm running dados or rabbets with my OF1400 is that the vacuum doesn't pick up the dust at the beginning of the cut, but does an awesome job with picking up the rest.
My assumption is that one of the issues is that the vacuum hasn't built up enough suction to draw the dust. If the vacuum started before the tool, with a delay from pressing the tool switch, this might help that little bit more with dust collection.
Maybe the CTs do this already...in which case I guess I'd have to buy one.
The tool start system implemented in the Fein vacs starts the vac as soon as the tool's trigger is switched, but this combined current draw reduces's the system's overall capacity. Festool delays the vac start a second so the tool's intial current spike passes. This bugged me at first untill I understood the reason.
I like your idea of delaying the tool instead but it could be very annoying leading to assumptions that the switch is faulty. Maybe if the slow ramp up to high speed was slowed down so you knew the tool was going, even though it took a few seconds to get up to speed, it would be acceptable.
Until then, what Seth said