MCI is not a set number and doesn't depend on where you work: Major City: LA, NYC, Chicago, Salt Lake, etc. MCI could be 3 patients if you are the first on scene with you and your partner; until you get help.
Where I work FT with 3 ambulance crews 4 days a week and 2 crews on weekends: with shuttle vans with 12 people in them, if we have an accident it would always be a MCI for us; Fire is right there with us, but 2nd and 3rd ambulance and more than 6 FF are 20 minutes away, (if we are lucky).
PT job has 2 or 3 crews on duty/on call. But 2 hours from closest hospital and 90+ minutes from help (40 minutes from helicopter help) makes life interesting: especially since we have 5 large hotels/casino's MCI is a real threat.
On the lightening strike scenario you need to be cautious when you are that far from help: My only lightening strike had 2 patients, and the one walking around confused but with good vital signs almost died where the one that wasn't breathing on his own, and bystanders were doing CPR when we got there did fine.
So if you and your partner start doing CPR on the pulseless/apneic patient who is going to watch the other 3 until help gets there?