With the advent of multilateration and ADS-B, it's now feasible for an airport to profile every runway movement and to provide its operators with timely feedback on their crews' performance. I know that LHR, for example, were looking at such a system a couple of years ago, although for various reasons it hasn't yet materialised, but I don't think it will be long before we see some of the world's leading airports doing continuous ROT monitoring.
We do record and analyse both landing occupancy and departing line-up times for every flight. Anything significant gets acted on pretty quickly nowadays.
To the OP, from the ATC point of view you need good use of conditional clearances (whether it be in a single runway mode or a segregated departure runway). Also a good appreciation of aircraft performance along with airport infrastructure. In a good headwind at LHR you could get a medium away in a 5nm arrival gap between two mediums for sure, possibly a heavy. However, sometimes I would struggle to get a medium departure away in a 6nm gap between two heavies early in the morning when those heavies have tired crew on board and everything takes a little bit longer, including vacating the runway. For a single runway operation, Gatwick has better positioned RETs for mediums, so the normal arrival gap for them between mediums is 5nm, I believe.
From a flight crew point of view, prompt line ups, which in the UK includes the ability, once in possession of a conditional line-up clearance, to cross the holding point before the one ahead is cleared for take off provided the following aircraft is departing from the same point (or behind).
Send me a PM and I'll see what we can find from LHR.