Renaissance Lucerne Hotel in Lucerne

We booked a 4-night stay for two couples (2 rooms) at the Renaissance Hotel by Marriott Bonvoy, Lucerne, expecting a true 5-star experience—especially given the premium price, which was even higher due to the New Year period. What we got instead was one of the worst hotel experiences we have ever had.
From the moment we walked into the soulless, tiny reception, alarm bells rang. But nothing prepared us for what followed. The lift, corridors, and rooms were absolutely shocking. This hotel is NOT a 5 star property—it is barely a 3 at best.
The corridors and lifts were filthy: stained carpets, dirty walls, and a general feeling of neglect. The rooms were old, outdated, and poorly maintained. There was dust and hair on the floors, the furniture looked worn and decades old, and the overall cleanliness was unacceptable for any hotel—let alone a supposed luxury one.
The heating barely worked, completely unable to cope with the cold, while wind came through the window. On top of that, soundproofing was nonexistent: we could hear every single noise from the hallway and outside, as if the window were open and people were standing next to our bed.
No slippers or bathrobes were provided—basic, standard amenities in any legitimate 5 star hotel. I had to ask at reception just to get slippers. Daily housekeeping was minimal and careless—no proper vacuuming, no attention to detail.
Speaking of attention to detail: there was a wall art partially hidden behind the TV, as if someone installed the TV without even checking what was already on the wall. This sums up the entire experience—careless, amateur, and laughable.
The rooms were very small and cramped, completely unsuitable for a luxury hotel. The only thing that looked remotely updated was the shower, which may have been renovated recently. Yes, it was clean—but that alone does not justify calling this a 5 star hotel.
Breakfast was also disappointing. While there was some variety, all hot food was consistently cold. We only ate breakfast 2 out of the 4 days, choosing to go elsewhere instead.
Because the booking was non-refundable, we had to stay, so we spent as much time as possible enjoying beautiful Lucerne and avoiding the hotel entirely.
Yes, the location is good—but so are many other hotels nearby that cost the same and actually deliver quality.
What is most disturbing is this question:
HOW is this accepted as a 5 star hotel—especially in Switzerland, where hospitality standards are supposedly strict? Who regulates this industry? Who inspects these hotels?
We are absolutely gutted to have paid this much money for such a poor, borderline unacceptable experience. This stay has completely destroyed our trust in Marriott Bonvoy, and we will 100% avoid this brand in the future.
This is clearly accepted by Marriott, and that says everything. When a company becomes this big, this wealthy, and this powerful, it seems standards become optional. What would never pass inspection for a smaller hotel somehow gets a free pass under the Marriott name. Marriott used to represent quality; today it feels like branding, money, and market dominance have replaced pride and accountability. Avoid!

This price for a room like this? Unbelievable!