LoCo airlines use computerised algorithms to manage fares. The more people are looking, the higher the fares go. The fares should settle down to a more competitive level once the initial hype dies down. For the dates I looked at in September it was well over £100 cheaper to fly DL to JFK using SkyScanner than DY to SWF and DL may have better seat pitch (DY haven't published their seat plans for the 73max yet
AFAIK).
In the past, I've often found it several hundreds of pounds per person cheaper (well over £1,000 for the family) to fly to the USA via AMS than flying from EDI via JFK, EWR, ORD or YYZ. DY is already making fares to the USA from EDI much more competitive which, in turn, should increase the market size. Interesting times.