I also have 4 personal friends that died from heart failure and cancer that were marked as covid.
I'm truly sorry for your loss.
Again, it depends on the doctor or examiner at the time and the circumstances. Covid is a vicious thing. It's not the virus that actually kills you, it's your bodies response to it.
Sick people, those with underlying conditions, have been stated as the most vulnerable to it since day one. Yes, your friend with cancer probably would have died of cancer at some point anyway, but I'm certain that having covid didn't help. That's why it may have been listed as the cause of death in that it accelerated the death itself.
If you're in the middle of having a heart attack and someone shoots you dead it's still murder. The fact that you were going to die anyway is moot.
And my wife's lifelong friend is a Ph.D. and works at the University Hospital at Boston College. She sees a lot of the same misinformation making the rounds, especially among those who have underlying conditions.
People simply want to believe what they want to believe. Add to that you have an entire movement of anti-mask, anti-vaccine nurses and batshit crazy doctors that are pushing horse de-wormer as actual treatments for covid and you're going to have a great deal of misinformation out there.
But there is no great conspiracy. There never was. At worst, it's difference of opinion.