Q. Can I ask what you are basing your certain level of performance on?
A. I should be able to make a judgement based on the aircraft type, operator, destination, conditions etc whether you can be squeezed off in the miniscule gap available between arrivals. This is sometimes very tight and can be down to (almost) split second timing. Poor judgement can lead to go-arrounds or worse. If the best of my information shows that I should be able to get you airborne in the space available, but you haven't told me that you are performing worse than normal, then I'll be a little upset (but not as upset as the guy on minimum fuel having to go arround on vapour).
We are well aware that you use assumed temperatures and de-rate power etc, but I don't believe the question was about that. I also don't think that there can be many places in the "civilised" world that don't have noise regulations for clinb angles to get you away from the NIMBYs ASAP. As for using the greatest amount of runway possible, I have never seen evidence of any pilot doing that (Perf A would also suggest otherwise).
What then is the answer?
Always use bigger gaps? That reduces the number of available movements (therefore unlikely), but is used for individual aircraft requiring it.
Tell the controller that you may need more runway? BINGO - takes 5 seconds of RTF time and allows the controller to set up a bigger space for you!
[Ramble off]