I guess the issue is I was assuming that witnesses will publish any adverse price move during the last hour (including at the current time). In such as case, I don't believe it can be gamed.

This would be a significant change in the existing practice for price feeds and would significantly increase the number of updates required (every time a new low is reached).

Also, no matter how often witnesses update, currently the median is only updates once per hour. That would either need to be changed, or you would need to use individual witness updates rather than the median, which increases vulnerability to deliberate or accidental bad feeds from a witness.