an accurate calendar that is 11 days short of a solar year and that pretends that in chutz learetz we don’t know when yom tov begins
It’s accurate. The chachomim were well aware of the solar calendar (certain dinim are based on it) and put in leap years so that it remains in sync over the long term.
No, we don’t pretend anything, but we do still keep two days. Learn the sugya if you’re interested to know why.