I do like this principle of allowing the separation minimum to "compress"
Leaving wake turbulence alone for a little while (it's an approved procedure) the 2.5nm separation is a minimum radar separation. To reiterate again the separation is allowed to compress only when the tower controller is visual with both the aircraft concerned. Separations maintained with Reduced Separation in the Vicinity of an Aerodrome, i.e. visually, are not subject to the same minima and hence this is not cheating.
It is commercial pressure encroaching upon safety.
Two aircraft less than 2.5nm apart on a clear day from a tower when both are established on precision approaches is perfectly comfortable. Issuing safe and legal landing clearances is the challenge and we owe a debt to the professionalism of the aircrews involved to expeditiously and safely vacate the runway, almost always with a great deal of situational awareness of what is occurring behind them. Of course, if it doesn't work, then a go around results and this too is a perfectly normal and safe procedure, albeit to the detriment of what the commercial pressure was trying to achieve. Oh well, in this case safety wins, and it's the professionalism of the controllers that does not allow the pressure to warp their assessment of any given situation.
In my opinion the 2.5nm rules as they are allow the maximum safe throughput of aircraft on one piece of tarmac in good visibility, still conveniently putting wake turbulence aside since this is a further limiting factor.