easyJet, BA and Virgin all did flying for TUI every year prior to this summer. TUI had around 20 aircraft planned for 3rd party this summer and only 6 MAXs (excluding delayed deliveries) that are grounded. So the remaining 14 aircraft works out at roughly 25%.
Thats my understanding anyway. I guess my main point was: TUI guys must be pleased that 3rd party can be scrapped rather than their own jobs.