This doesn't necessarily seem like it's a guarantee - firstly, from my experiences working private ambulance, most are built and staffed to operate at or near capacity, as idle ambulances don't make money.

Depending on the location, when you dispatch ALS/BLS ambulances this way, whose medical license are the EMTs and paramedics working under? Does the county medical protocol director like/want this?

In cases of cardiac arrest, you're going to typically want more than an EMT and a medic on an ambulance. CPR is, as you know, a man-power intensive activity.

The three things you mention are not really problems in a 'modern' PSAP. "911, what are you reporting?" "Confirmed cardiac arrest". Even without that, in most areas around here criteria-based dispatch is used to determine ALS/BLS with an erring towards ALS if there's any question.

In my county (Washington state), the protocol states (and is met with 94% reliability that from call reception for EMS, dispatchers should have toned the appropriate unit(s) with 60 seconds of call reception, and those units should be en route within 2 minutes of that (even for in quarters response).