Data point.
last time (more expensive than this time) Oman Air downgraded everyone to economy unless you paid a lot more.
That was bookable on Oman's own website (as I did). And seat mapping was business class with no issues whatsoever.
They contacted me & downgraded mine with just three weeks to go after booking several months in advance. Left me out of pocket as I started to book hotels (and some onward internal flights) once we were within 4 weeks.
They can't be trusted and could not care less that it was completely their fault

Perhaps a few who booked and flew within a week or two got away with it.

[PREM FARE GONE] WY: MXP-BKK rt Business Class 1072€