I do think that unless a teacher is MG+ themselves it would be very difficult to have a real understanding of what being gifted means. To take reading for example, in my experience I don't think many teachers really grasp what it means to be able to read Harry Potter at 6. Because it's not just about decoding (as we all know), it's about what they can do with that information and how asynchrony influences their interpretations and then how that then influences their play and interactions with others. I have explained that to people in the past and you can see them thinking I am just making excuses and trying to connect the unconnectable. They don't see it and, I suspect, can't see it.
Similarly with maths abilities. In Australia teachers with strong maths skills are identified as in poor supply. Teachers have seen what dd can do with maths and even then, they don't believe it. It's like she's performing a magic trick. And so if teachers are uncomfortable with the subject matter that too can influence their understanding of how giftedness matters.
Some very limited anecdotal evidence - friends of ours, both teachers, regularly talk about one of their nieces who is 9 and would rather read physics text books than play with her nieces and nephews. One of this couple, an identified gifted man, supports the girl's choices. His wife, who is lovely and smart enough but perhaps high average, doesn't get it and thinks it's unhealthy.
The two teachers dd has had any involvement with, who have 'got' the giftedness thing, I have later found out have gifted kids themselves. And so they have understood (either directly, through their own likely giftedness, or indirectly having to gain an understanding of their children) that giftedness is not just about having a skill, it has much broader implications.
I don't mean to imply that teachers are not smart - just that it's our natural inclination to think that other people think like we do ourselves. For some kids teachers with a normal level of understanding are absolutely fine, however for a lot of kids - not just gifted, but kids whose thinking is unusual - I think that can cause problems. What you can realistically do about it I have no idea.
Anyway, just my thoughts!