The good news is that plenty of Marriott Bonvoy full-service and luxury properties provide excellent breakfasts to Platinum Elite and above. My wife and I recently stayed at five properties in Italy -- one Westin, one Renaissance, two Autograph Collection, and one St. Regis -- which all had well-stocked breakfast buffets with plenty of choices and no extra charges for anything.
Depending on the brand and property type (hotel or resort), the daily breakfast benefit rules (for member + 1) at full-service and luxury properties fall into three categories: (1) breakfast through "Guaranteed Lounge Access," (2) breakfast in the restaurant as a Welcome Gift choice, and (3) no breakfast benefit at all. See the
Marriott Bonvoy Loyalty Program Terms & Conditions for all the details.
When there's no lounge or the lounge is closed, hotels of Marriott legacy brands that provide restaurant breakfast through "Guaranteed Lounge Access" can limit the free elite breakfast to a "continental breakfast." In such cases, the hotel can offer a more complete breakfast for an additional charge. Most hotels realize this is petty, so they provide a full buffet or traditional hotel breakfast. But they're not in violation of the T&Cs if they only provide "continental breakfast" and offer a credit toward other breakfasts.
The benefit should never ONLY be a discount or credit. If there's only a credit -- insufficient for breakfast food, coffee, and juice -- then the hotel is in violation, and the member should invoke the guarantee.
If a full-service hotel only wants to provide daily USD $10 credits for member + 1, then the hotel should rebrand to Courtyard, AC Hotels, or Moxy.