"Why do they take a ladder truck to medical calls?"

The EMT has two or three people trained to take care of the actual medical issue(s).  

Who puts the person on the backboard?  The one who weighs 253 pounds. 

Who do you think carries the injured/sick  person to the ambulance? 
 
Who do you think controls traffic at the accident/shooting/medical site?
Who do you think cuts the victims out of the cars?

How does a driver maintain the skills to drive a multi-ton vehicle in a town or anywhere else?  

"Shouldn't the funds match the percentage of types of calls?"

How much does a fire truck and all its equipment cost compared to the ambulance?
Every fire fighter needs the breathing apparatus and turnouts to fight a fire.  
You can't fight a mill fire with the two or three people in the five ambulances mentioned in the article. 
All those people have to be trained.  That takes money.