HFK - to summarise, if you were 5nm behind a heavy when it touched down (which I am happy to believe), you weren't 5nm behind it at top of descent.
From your example, 5nm behind at 2.5 nm/min is two minutes between arrivals. 2 min spacing at cruise, say 7 nm/min is 14nm at top of descent. Please bear in mind arrival sequence distance has nothing to do with ATC rules, procedures, or abilities. It is down to how long you take from landing clearance to clear of runway.
Capn Bloggs - unfortunately, as far was I know, we never go back over bad arrival gaggles to see what went wrong. This and the fact we reward the rouges I think is a major failing on our part.
If METRON gave you unachievable times it would be pretty useless, and its from 'merika where they have real traffic so it can't be
ETA
Hazard Alerts out again for traffic holding today
That should be treated as an 'incident' and investigated.