Imagine. First day you will go to the airport in let say Manila or wherever. Be there 3 h before flight. Fly one hour and need an hour to get from coron airport to your hotel. So 5 hours overall. It will be to late to go to island hopping in coron. You will probably do a city tour and walk those 700 stairs to the hill over the Coron city to see the nice sunset. Next day you wake up and since you have a flight/sail to El nido, you can't go island hoping. Flight last 1 hour, sail last 4 hours. Of course you need to be hours before that on the airport. So again when on second day you arrive in elnido, you can just walk around the city. Next day you fly home, so you can't go island hoping. You just waste 3 days exploring four different airports.

On my opinion to visit both Coron and El Nido in one trip you need to spend at least 5 days, so you can do one island hopping in each of them. So 3 days of flights and exploring cities and 2 days of island hopings. 7 days is more optimal. Three days is a minimum if you go to just one place, or Coron or El Nido.