IQ doesn't matter. Every child deserves opportunities to learn and grow, opportunities that match their aptitude. There's no need for an IQ test when providing that. IQ testing is just used for gatekeeping.
In theory, as long as we have some reliable way to measure the aptitude, and we provide the corresponding opportunities, I don't really mind if we avoid mentioning the word "intelligence".
But, you know, the offensive thing about IQ is exactly that it demonstrates that different people have different aptitude. So, in practice, I find it difficult to believe that people fighting against the concept of IQ would be willing to provide sufficient opportunities to children with high IQ.
Sadly, many people's instinctive reaction to a gifted child is throwing some obstacles in the child's way, to "prove" that the child "was actually not that smart". (This is even more likely, if the child is a minority, or autistic, or different in some other visible way.) Some of those people are teachers. I know stories...
Like, there is a girl I know who did math olympiads at elementary school. For some reason, this rubbed her math teacher the wrong way, so the teacher started bullying her in the classroom. Two years later, the girl had phobia of math, and was unable to do even school-level math. Then her parents intervened and transferred her to another school, and with some private tutoring (by me; that's how I know the story) she became a straight A student again, and later successfully completed a university that required a lot of math. She never got back to the competition level, though, because the wasted time made a difference.
This story is less rare than you might hope. Quite many gifted kids, unless they also have superior social skills, are bullied either by their peers or by adults. People are bad at tolerating difference; twice so, if the difference suggests that the different person is somehow superior. And the gifted kids with superior social skills aren't winners here either; when they tell you "I was interested in many things, but I was careful never to mention it in front of my classmates", it makes you wonder what they could have achieved if they were allowed to follow their interests freely.
IQ matters in terms of determining the spectrum of offerings that a funding-limited school system (which is all of them, just to different degrees) should provide.
If you measure achievement based on "percent reading at grade level and passing MCAS", then all high-IQ students are, in effect, "left behind". I agree strongly with your 2nd sentence, but disagree strongly with the first and fourth.
