There's a significant difference between COVID-19/SARS-COV-2 become endemic, and it continuing as a pandemic that threatens public health systems due to caseload density. Yes, we're unlikely to get beyond it being endemic, which means that like influenza, it will continue to be an issue, but we can certainly get a point where it is "just endemic", which would be a huge improvement over the current situation.
How frequently do equivalent Flu mutations occur?
Well, there is, we just don't want to pay for it: vaccinating poor countries, where effectively the mutations are being created by high infection rates.
Why would the current crop of vaccines be able to stop the virus, even if applied worldwide, seen that they don't prevent infection?
The evidence is still not solid on whether or not it does this, as far as I am aware.
Also there haven't been enough variants as to determine that most variants are coming from poor countries. Speaking of delta, India has more population than the entirety of Europe. Mathematically it makes sense than a variant could come from there regardless of whether the vaccine does anything.
It has greatly slowed the spread. The highest vaccinated countries have almost stopped it. There is every reason to believe that high vaccination across the world would stop covid, and anything less will ensure continued spread (and mutations).
People demanding an all or nothing from a vaccine are missing the big picture.
Israel has faced waves of 3 different viruses - original, Alpha and Delta what have required different level of immunization and Israel has managed to vaccinate itself out of 2 of these waves.
Looks quite impressive to me.
I also fail to understand why people pretend that 2 doses should be expected to stop Delta that has higher viral load - it does not make any sense.
It is a probabilistic game - antibodies are not smart - they are like mines - you need to have high enough concentration to stop viral particles to move around. If the viral particles can overload this concentration - they are going to win. There obviously must be some threshold of antibody concentration below what you can't avoid infection - when 2 dose regimen reaches it too quickly, well, game over. 3rd dose regimen is known to boost antibody concentration and keep it high for longer time. There is no surprise here and yet even people in position (like WHO) that should know better have intentionally ignored it.
Stalling the spread is useless as well - we have already had two major mutations in less than two years.