This is my personal opinion so the only evidence I have is personal experience of which I have 57 years. I don't intend to quote everything I have experienced in that time to justify what is only my opinion, but here's a couple of reasons I say that.
My mum was offered Thalidomide whilst she was pregnant, the only reason she refused it was that she didn't suffer from sickness at all. If she had been sick I would have preferred her to take natural remedies such as ginger or peppermint. It was said at the time that the drug had been properly tested.
I suffered from atrial fibrillation for 2 periods of around 2 years each. I had 4 short stays in hospital for treatment and was on some very potent drugs. One of these has potential side effects of blindness and death. I agreed to take it because I was so breathless I couldn't bend to put shoes on or walk a very short distance without having to stop for breath. Since than I have discovered that when my heart goes out of rhythm all I need to do is take a dose of a magnesium supplement. This is a supplement of something my body needs and is lacking. If I'm lacking a nutrient then no amount of drugs will give me that so they won't cure me whilst a supplement may.
My supplements were recommended by a qualified naturopath.
No doubt you believe supplements to be better than drugs based on your personal experience, and that is fine. We're all entitled to our opinions and we don't have to justify them to anyone. However I was curious about such a strongly worded statement as "Supplements have to be better than drugs surely?".
Anyone can cite the case of Thalidomide, in which it is clear that the drug was unsafe, despite being approved for use in pregnancy. However, the systems in use today are far more reliable... of course there is no guarantee that it couldn't happen again, and indeed, every few years there seems to be a drug that causes severe harm or death in a small number of people and the drug is withdrawn. There are thousands of drugs used safely and effectively by millions of people. On the whole, the system works. Non-drug products can also maim and kill, but we don't hear much about that because anyone can sell these products without the same level of oversight as drugs have.
I know very little about cardiac care but does your doctor agree that all you need to stay healthy is to take magnesium, and that magnesium would have been enough during that earlier time, without any of those other drugs? I think if your belief about it is correct, then you are very lucky to have found something that works for you. I think if it was the case that all the people with that condition could be treated with magnesium alone and never needed the other drugs, then all the cardiologists would be testing and prescribing it as a first line treatment and the other drugs would no longer need to be prescribed for that condition.
I consider magnesium to be a pharmaceutical product anyway, because it is produced by drug companies, can be measured and quality assured like a drug, and is subsidised and provided in hospitals and (in NZ, the publicly funded pharmacy services). I don't treat it as a "supplement" like, for example, ginger, peppermint, chromium, or CoQ10. I'm pretty sure there is scientific research evidence about magnesium, as it affects a number of body systems.
"Supplements have to be better than drugs surely?" is not a statement that can be applied across the board. Many drugs are the only effective treatment for certain conditions. In some cases, supplements have a beneficial effect, but it is not as strong as a drug. In other cases, a supplement has a negative effect, especially if taken with a certain drug.