It doesn't matter that the ticket was ex EU; the EU regulation applies to all flights departing the EU

any passenger on an EK flight from LHR/AMS/DUS etc to DXB is covered
No passenger on an EK flight from DXB to Europe is covered

If flying on an EU carrier , then would be covered on any flight to or from the EU

The legislation also requires that airlines provide assistance such as accommodation when a flight is delayed or cancelled for any reason as well as provding compensation should a flight be significantly delayed ( for most flights from western europe to dubai , EUR600 if delayed 4+ hours ) due to things within the airline's control

If thinking that this is an unfair rule , cionsider how some airlines treat passengers when not forced under this type of legislation

e.g. in USA, get delayed due to weather and airline just says "not my problem, sort your own accommodation out"

e.g. With EK, get downgraded on a sector, may actually get no compensation at all ( see some other threads for examples )

e.g. with QF , flight gets cancelled and so delayed, zero compensation

If all airlines in EU had been treating passengers properly, then legislation would not have come in.

For downgrading; this is something where a large compensation is fair imo since it is the airline's choice if it operates a flight with an aeroplane without the cabin which was paid for or oversells the cabin

With business passengers , there is an opportunity for airline to avoid compensation by upgrading if oversold , it is only with 1st class where there is nowhere else to go

Downgrade compensation is high, but I would suggest is the easiest thing for the airline to avoid having to pay out : don't downgrade people, it is something completely within the airline's control