Marriott can just change the peak/offpeak/standard on the fly without any warning. It only encourages folks to have more speculative bookings. Some say this is not ethical. I do not think Marriott cares anything about it. Clearly Marriott does not have a good reputation any longer with the category change in 2020 and the introduction of peak/offpeak during the pandemic.
It is very hard to use the 35k and 50k FN awards with the peak change....