I'm a little confused as to which point you got yourself confused at, then made up stuff to fill in the blanks?
Now, I see your name is son-of-satire so maybe that explains it, but for the sake of anyone reading, I'll have at it.
There is no common sense reason why multiple waves can't get bigger. I think the confusion lies in the fact that the virus can move around the country, yet the country counts the total as a singular thing.
For example, the north of a country can be highly infected in wave 1. Then, later, the much more populated southern half of the country gets infected when the north has already had its wave and most people have decent immunity. Unfortunately, the south is more populated, so the second wave, even though the north is not counted more than a handful, is much larger.
Then the extremely populated East gets hit, the north opens up from lockdown, the south ignored the lockdown rules totally, and 2 weeks later you have yourself an even larger third wave, because, like I said, as a country, you count the North, South, East and West as one lump total. (presumably, the west followed rules without complaining about freedom and so 0 people got infected in this example)
I hope that helps.
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To address another point, there is no absolute proof immunity is long lasting. In fact:
It's not known if people who have only mild symptoms, or none at all, will develop a sufficient adaptive immune response.
The immune system's memory is rather like our own - it remembers some infections clearly, but has a habit of forgetting others. Measles is highly memorable - one bout should give life-long immunity (as the weakened version in the MMR vaccine does). However, there are many others that are pretty forgettable. Children can get RSV (respiratory syncytial virus) multiple times in the same winter.
Then, comparing to other Coronaviruses:
Four produce the symptoms of the common cold and immunity is short-lived. Studies showed some patients could be re-infected within a year.
Research at King's College London also suggested levels of antibodies that kill coronavirus waned over the three-month study.
What you're doing is building a conclusion based on what is little more than an old-wives tale / poorly done educational system, based on something that 'seems to make sense' - the idea that once you get infected, you can never be infected again. Which is just not true.
Herd immunity can work in small pockets for diseases that do go away after one time, like chickenpox parties creating herd immunity among the local kids. But how come chickenpox is still around? Because it spreads easily enough to be able to hop around the country quietly and slowly enough to continue infecting the uninfected for years to come without major government intervention (because it's not deadly if you get it as a child).
Unfortunately, CoViD is deadly, it's not seasonal, it's global, and it's something you very, very much do NOT understand in any sense of the word; logically, scientifically, or politically
As far as COVID 19 being deadly, I think time will show that far less people died this year of all causes than had died last year or the year before. A deadly pandemic would surely kill more people than normal life and death situations have killed using year on year comparisons.
The deaths due to bacterial pneumonia, economic strife and psychological tragedies as a result of COVID 19 measures will surely be felt for at least a decade to come.
The number of excess deaths is indeed a clear indication that far more people are dying than a normally given year, but that's not even the only factor. People getting sick isn't always just getting a cough and then moving on.
People I know personally have been stuck with chronic suffering for months after contracting the virus, other people now have permanent damage to their bodies, and so on.
You also have other people dying because hospitals are overwhelmed. You might say 'but the hospitals are empty' or not at capacity, but in some regions in the US - I believe california hit the news lately for it hence their lockdown, hospitals are at capacity. Then consider other countries that aren't as well equipped as the US or Western Europe.
Then consider how India has a logistic nightmare that could take years before the vaccine is fully distributed, making the entire process useless for them as the virus shifts around like chickenpox.
You can keep making excuses and blaming the breakdown of the economy for deaths or the flu, and to some extent these are true; people do die from the flu, people do die from poverty. And more people may die from those things in this current times.
But that doesn't mean you can say these things outweigh direct damage from Covid. even 0.5% deaths of 1 billion is 5,000,000. 5% critical is 50,000,000. 15% severe is 150,000,000 people in need of oxygen tanks.
You'll need a good few doctorates, a lot of research funding, and a ton of imagination to prove these numbers are insignificant to society.