I had many similar concerns when my (now 7 year old) son was heading to kindergarten. Our approach was to pursue a school that valued character development and artistic expression above academic rigor. His kindergarten/first grade teacher (they do 2 year loops) didn’t focus much or differentiate in his academic strengths, but she did absolute wonders for him in his social skills and emotional control.
As our son made social/emotional progress, we would slowly advocate for more challenging academics. It is very easy to get caught up in the amazing things your child can do, and want to race them ahead even further. Early elementary, at least in my opinion, is a time to build that solid foundation of character. There is plenty of time ahead to adjust and accelerate. Now, my child may have needed more help in social skills than yours.
Progress in advocacy has felt very slow. I have spent many many hours wondering if public school is the right fit for my son. In our case, taking it slow has been a giant help. He has had time to develop, to gain a love for sports and acting, and to form friendships. Going into 3rd now, and the school will pull him into 5th grade for math and leave him with his peers for the rest.
As for your specific questions:
1) definitely speak with the teacher. Don’t be surprised if they don’t find it as impressive as you do. There are many things a teacher will be looking to develop, and math is pretty low on their list. Gentle advocacy and supplement material at home.
2). Trust your instincts on what would work best for your children. Not necessarily what is best for them today, but try to Take the long view of what makes them the best adult version