"Turnover is over 80%!"

That's a big red flag. Given the negative content of most of the rest of your post, I'm not surprised by that statistic.

These days, most schools in the PRC try to hang on to their FTs longer than they used to. That's because the new visa regulations mske it a cumbersome and time-consuming exercise to hire new foreign staff.

Teacher turnover of over 80% is excessively high. It suggests that most incumbent FTs either don't want to renew their contracts or that the visas they hold cannot be renewed.

A school in the PRC that treats its FTs well will probably have an annual FT turnover of 20% or less.