If you mean that there's not a single elite breakfast standard across all hotels and resorts of the Marriott "chain," then, yes, that's true.

If you mean that there are no standards by brand, then I would disagree.

There are essentially six ways that that Marriott Bonvoy hotels and resorts provide (or do not provide) breakfast to Platinum Elite (and above) members. See the following wiki here on FlyerTalk. Bs sure to click on the "Show more" link in the lower left corner of the wiki.

FAQ : Marriott's "breakfast offering" explained, by brand and by Bonvoy elite level

The wiki is not a substitute for the Loyalty Program Terms & Conditions document, which is updated often and which has an excruciating level of detail about some things, while failing to define such essential terms as "breakfast in restaurant" and "continental breakfast." These terms are used deliberately in the Terms & Conditions and apply to specific brands.

I have no problem with the purpose of this thread. There are occasionally properties that provide less than the published benefits. Marriott should not allow this. Such properties deserve to be called out.

However, complaining that a Renaissance Hotel would only provide breakfast in the lounge and would not honor breakfast in the restaurant as a Platinum Welcome Gift -- or complaining that an AC Hotel would only provide a daily $10 F&B credits for member + 1 instead of providing a full breakfast -- just shows that the someone is not aware of the actual breakfast benefits by brand.

On the other hand, when a Sheraton only provides breakfast in the lounge and refuses to honor breakfast in the restaurant as a Platinum Welcome Gift -- or when an Autograph Collection property without a lounge provides vouchers that only partially pay for breakfast -- those are legitimate complaints.

I've had good luck in recent years with Marriott Bonvoy properties honoring elite breakfast benefits, often providing buffets with outstanding selections (especially in Italy). I realize not everyone is so lucky.

Ideally, when a Platinum Elite (and above) member logs in to Marriott.com and looks at a property, the website would show how that property honors elite Lounge Access and Welcome Gift benefits. It would go a long way toward ending misunderstandings and disappointments. It would even be a good marketing tool when an elite member is comparing a Marriott Bonvoy hotel to a competing hotel. Unfortunately, Marriott.com lacks this useful feature.