As an observer LHR and JFK are chalk and cheese.
LHR highly regulated approach regime, always essentially standard IFR procedures whatever the weather GA traffic mostly kept out or strictly on for example a designated heli route.
JFK- more reliance on visual approaches and handling loads of traffic ( helis etc) that wold simply be face with a keep out not welcome here signing the UK. I have never heard a US controller say something like " remain clear of controlled airspace due controller workload" to GA traffic.