So it's not exactly that I'm dismissive of the MAP scores, but that I have a different sense of their limitations. Here's some anchoring data to work with: the following document details all of the skills that may possibly show up on a MAP K-2 assessment:

https://www.nwea.org/resource-library/map-growth/map-growth-k-2-assessment-content-common-core-2

Note that the highest mathematical skills that can be assessed are things like multiplication by a 1- or 2-digit number, division out of 100 or less, fractions to the 1/8.

The reading assessment is similarly limited to skills like CVC-e, R-controlled vowels, and consonant-le.

In other words, the ceiling on the MAP K-2/3 is pretty low. Your DC's scores are at the median for 3rd grade--which is above the design of this level of MAP, and well in the low reliability/high error upper extreme of the test, which means you won't be able to measure progress anyway. But it isn't really reasonable for a school to skip right over the universal screening instrument on the very first formal school experience of a student (fall of kindergarten, after all), in order to give them an out-of-level test, as they then don't have any data-based support for the decision to do out-of-level testing (even if this were in any way a routine occurrence--which it's not).

So, yes, in some ways, of course it's a lost opportunity, but at the same time, there isn't any really good information that can come from a MAP test score at the ceiling of the overall K-2 instrument that you couldn't have gotten otherwise by observing that the student can read fluently and do division--both known third grade skills. Any primary grade teacher could tell you that without standardized testing.

On a more practical note, I would consider a conversation with your DC's teacher about whether the school experience so far has been a happy and growing one in non-academic domains, and to explore instructional challenges that might arise out of a more direct curriculum-based approach to progress monitoring. E.g., a better measure of placement and growth would probably have to start from placement testing (there might be an actual test, or the teacher could use end-of-unit/chapter tests) using the actual math/reading curriculum used up through the elementary grades.

The current MAP scores tell you only that he is way above grade level. Curriculum-based assessment would have a better chance of telling you where his instructional level in this school system should be, and whether he is progressing at his instructional level. (If you can convince them to do so, he could also be moved to the elementary level of the MAP, probably next fall, recognizing, though, that the format is less developmentally-appropriate.)

And in the bigger picture, if he's happy and learning other kinds of new things this year, there will still be plenty of opportunities for him to pick up the pace academically in the future.