I am asking because I am genuinely puzzled by the constant referrals to 17.5 and 13.5 1s classes being "too fast".

Are American tracks really THAT small?

I ask because my home track is about basketball court size and despite being very low grip at times can handle 10.5 1s OK when the grip is there and I think would handle 13.5 or 17.5 quite easily. Depending on the layout we choose, lap times can be as low as 9sec and as high as 15sec with 21.5T TC