I think the hospital were nothing short of useless and you was lucky in there not to have an acute heart attack and die. I assume they relied on clot busting medication and you was very lucky it worked. If it was broken calcified plaque that caused the blockage, the medication would have no effect and you would have lost a lot of heart tissue life. The blockages seen afterwards 'could' cause a major heart attack if they break, but it's not likely. Statistics show the smaller blockages cause more heart attacks. Kenkeith has large blockages which haven't caused major heart attacks, and I had some for many years. So I'm not sure they were correct saying you was luck to escape with those large blockages.
The first visit to the doctor who stated you had a heart attack should have taken a blood test and that would have markers that would identify a heart problem or not. Did you have relief from your symptoms at the time of hospital discharge? What were the medications?
If you continued to have chest pains there should have been a stress test. Many years ago I had had a heart attack and ICU for several days with congested heart failure. I had stent implant, and 100% blockage of an artery and 70% blockage in another and discharged from the hospital. Going on more than 6 years I have not had any problems with medication.
I don't believe the first cardiologist was irresponsible. Your second doctor relied on additional information obtained by your then current medical status, your prior medical experience and treatment.