You may not have magically popped up from nowhere but the aircraft that departs from a considerably closer aerodrome did. Giving delays a long way out (as per ALOFT into SY) works well when the arrivals are well known and orderly but once things get busy and less orderly it becomes harder to manage.
You might be able to lose 18 minutes flying PH to ML but we then have to get you through the six aircraft holding ahead physically but landing after you. Far easier and safer to do it first in first out.
Also once you've lost that time there's no way to make it up if the sequence changes drastically such as LAHSO becoming unexpectedly available. Fabulous, you lost your 18 minutes. Pity that in the end you really only had to lose 6.
In the end, yes your magic box can work miracles, unfortunately the magic makes no allowance for the other 53 aircraft doing their own thing too. You're just as likely to run up the @rse of the guy ahead because you chose to lose the time on descent and he was doing it in the cruise. Until all that can be coordinated it's down to a decidedly basic box of tricks called me!