Someone told me IELTS is overrated.
In Vietnam there is certainly a section of people who treat an IELTS certificate as a mark of status. But the fair position is this: it is overrated, and you should not underrate it either.
What it actually is
It is an English certificate. That is all.
So somebody with band 8 and no teaching qualification is not thereby a good teacher. They can share how they studied, but going straight from band 8 into an English teaching job is a mistake.
Equally, using IELTS as automatic entry to something is not what it was built for.
So why do governments require it?
Not out of stupidity.
Plenty of people arrive without a word of English. They do not know the law and break it without realising. They get pulled over while driving and cannot speak. Some are involved in accidents and cannot communicate at all.
At that point, the police are legally obliged to hire an interpreter. Interpreters cost money, and that money comes from taxpayers.
So the requirement exists to prevent the situation arising: you need English to a certain level before you come.
Why IELTS specifically
There are plenty of other certificates; IELTS is not alone.
But credit where it is due: IELTS measures a learner's real level accurately. That is why it gets chosen.
In short
Do not treat the certificate as sacred. But do not dismiss the number either, because it describes fairly precisely how much of your life you can actually run in that language.