With respect specifically to Marriott points, I do not find that to be the case.

These "Marriott points are worthless" threads crop up regularly, typically sparked by a single instance of frustration that there are no points bargains at a particular destination on a particular date. As can be seen by the many contrary responses, that's really not true as a general proposition. There are still many excellent uses for Marriott points, which have overall held their value relative to cash prices. It's actually a bit surprising to me that the value's still there, as there are plenty of instances of traveler loyalty programs where points have been materially devalued (e.g., UA, BA).