When I've stayed at the Sakura the first time, breakfast was also served in the restaurants. That's actually much better than in the lounge, assuming you can get a seat without having to wait too long (the restaurant is rather small as I remember). The quality and ambience was excellent in the restaurant.
Well, these are strange times. We had the breakfast in the restaurant, but the buffet was gone, replaced by a Japanese or Western set menu. Arguably an even better ambience as a result, but I missed all the items that were no longer available as a result.
I have a reservation for next month during Sakura season. I'll report back on what it's like then if I go through with it.
Note: I'm only Gold with Marriott, but I am Platinum with SEIBU PRINCE CLUB program, so I am guessing that benefits will be similar to Marriott Platinum in this regard.